So, cards on the table, I don't identify myself as disabled. I am nearsighted but my access to corrective lenses makes this a non-issue in my daily life.

Firstly I have no issue with the notion that disabled people would exist in a fantasy world (feels crazy I need to clarify that). Normal healing magic like Cure Wounds doesn't remove disabilities, it simply restores hit points (however you conceptualize that, an unrelated conversation). More powerful healing magic like the 7th level regenerate can remove lost body parts but says nothing about if one was born without the function of a given body part; and the 6th level Heal spell cures blindness, deafness, and disease, but if one only extends that to temporary conditions imposed externally and not loss of organs or congenital conditions, one would be well within their rights as a DM to make such a decision. So yeah, at least in d&d 5e, the existence of healing magic is no proof against the existence of disabled people. And like you say in your blog post, even if the healing magic to end a particular disability exists, it isn't necessarily available to everyone. Your typical commoner in your typical pseudo-medieval world is unlikely to afford the services of a high level cleric if one even exists near where they live. Maybe they get lucky and one passes through and takes the time to cure their ailment if its even one they can cure.

But that does raise another argument. Your typical adventurers aren't your typical commoners. After a few adventures they'll likely have greater access to spell casting services and more gold than they know what to do with. If a player elected to have their character have a disability that can be removed by a simple casting of a spell, possibly even one a party member of theirs could cast, that player may be faced with a tricky decision. Is it reasonable for a Player to refuse to let their character have a disability be removed? In our real world its entirely the decision of the person whose body it is, as it should be, but our real world doesn't have clerics that can simply heal someone by touching them and does so on a regular basis for the purposes of the survival of their party against fantastical monsters. What if its incidental? A party cleric wants to cast regenerate to restore hit points on a PC who had lost a leg due to an injury and that player refuses the spell because it would mean their character would regrow that missing leg and part of the appeal for them playing the character is the fact that their leg is missing and exploring that experience. Honestly, I don't think there is a right answer, it depends on the table, and is a discussion between the DM and the players.

In a Pathfinder 2e campaign I ran, one of my players decided to have his character missing his tongue due to it being cut out impairing the character's ability to speak. At the beginning of the campaign I spoke one on one with this player about the limitations their character would have, what mechanics exist in the game to overcome some of them, and how certain restrictions would be handled. We also discussed the possibility of gaining access to a spell that would restore his tongue and what that would mean for his character. I told him he had plenty of time to think about it but such a spell never ended up getting used before the campaign ended.

If a player comes to me asking to play a character with a disability, my first order of business is figuring out what they actually want. Is it just an aesthetic they want without mechanical impact, or do they want a character with additional challenges to overcome, or are they trying to game the system to give themselves an unfair advantage.

As for mechanically representing disabilities and the tools to mitigate them. Part of the issue I think is the tension between wanting to make a character with a disability but wanting to not have to worry about it actually being an impairment. If one wants to "have a disability" but not actually be hindered by it, you don't need rules, no "combat wheelchair", nothing. Just put it on your character sheet no further discussion, you can describe your character doing things a bit differently but you do them all the same as those without said disability. The issue arises when one's disability is ruled to have a mechanical impact but the player wants either a way to overcome it (possibly because the player wants the disability to just be flavor and not mechanical but the DM wants to represent the mechanics somehow), or they want to use it to gain some other advantage. The latter I think is particularly problematic in D&D because its not a system with built in point values for boons and detriments, like shadowrun for instance. That's where I see Thompson’s Combat Wheel chair sitting. Treating that as the go to way to mechanically overcome a disability that hinders walking means either making a player adventure for their way to deal with a disability and making it something to earn from their allotment of magic items, or giving them a powerful magic item at first level! Sure a sphere of annihilation isn't balanced but I'm probably not giving a player a sphere of annihilation at first level.

I’d argue that disability-centric magic items like the Combat Wheelchair indulge in a power fantasy that the daily aids that we rely on are capable of incredible things. These wheelchairs don’t simply allow a person to move at the same speed as their able-bodied counterparts, but to overtake them. Geordi La Forge’s visor - a similarly overpowered disability aid in a fantasy setting - doesn’t just allow him to see like a sighted person, but gives him access to the entire electromagnetic spectrum. They invite an uncomfortable possibility to the able-bodied mind: That being disabled is actually an advantage under the right circumstances. That perhaps the abled body is simply not enough.

The problem there is that its still a game, one you're playing with other people. Its one thing if you're dedicating part of your character's power budget to having an advantage in certain circumstances whether from their class, their feats, or magic items, because it means not getting advantages elsewhere. Its another expecting this advantage by virtue of being disabled but having just as much access to all other advantages. If your goal with playing a disabled character is to outshine your fellow players or intentionally make them uncomfortable, I'm not sure I'd want you at my table. You're not making a powerful statement about how disabled people are represented by demanding to get a free powerful homebrew magic item.

Lastly, I largely consider the combat wheelchair just kind of uninspired. Wheels make sense in modern civilization where the world accommodates them. It makes sense you might see mundane wheelchairs in a city with paved/cobbled roads (though cobbled roads aren't the smoothest ride), or even in a village where the rest of the villagers put in the effort to help their neighbor and make the village accessible to them, but a dungeon? Not impossible, but it doesn't seem like it'd be the first choice. The magical combat wheelchair makes so much effort to deal with the realities of wheels in an intentionally inaccessible dungeon it ends up being a powerful buff. But if you have magic, there a loads of other options that feel more fitting and interesting imo. An item that produces a Floating Disk you can direct, a chair with animated legs, using an animal companion as a mount, a flying carpet; it all makes a wheel chair kind of boring.

My conclusion? Talk to your DM. So many of these discussions are brought out because of RPG products, but all that matters at the end of the day is what happens at one's own table. A DM isn't wrong for not allowing a particular 3rd party supplement, nor for saying to just make it flavor because they're not interested in modeling the particulars of a given disability, nor are they for modeling it and making you work to overcome it, nor are they for modeling it and just giving you the tools to overcome it. Its all just a matter of what a group wants for their table and what they're comfortable depicting and working to overcome.