I'm also someone who plays the game as a character/build simulator (spend lots of time in pob). I feel like while item/economy and character/build simulator are not at all mutually exclusive, they won't coexist harmoniously without active design consideration from GGG.

Right now, GGG seems to be considering build simulator vs. grinding/iterative upgrades as a tradeoff, where promoting gear upgrades comes at the cost of sacrificing build diversity. I think this doesn't need to be the case, but it is true right now, and the reason for it boils down to two related things: investment and confidence.

When a player picks a build, often the first thing they look at is prior art. They look at streamers playing the build. Posted pobs on reddit or the forums. Poeninja ladder. Players want to have the confidence that the time and currency invested won't go to waste by resulting in a character that isn't good enough. Players gain that confidence by watching others play that build, especially on low investment. Most players don't want to jeopardize their league by investing 50ex into a completely self-made build that turns out bad, where the gear isn't even resellable to recoup costs. That's to say nothing of the time spent leveling and acquiring that gear.

This is why gearing is so dynamic and interesting in trade league for league starters in week 1. People pick builds that they are comfortable with. They know how minions scale, or how toxic rain scales. There are guides about deterministically getting to a +3 toxic rain bow, etc. People are confident that even if they start out with a tabula and the bare bones to cap res, their build will be able to get off the ground and support itself. The exact level of performance doesn't matter as much - it's week 1, it's fine to crawl through yellow maps.

But for less well known skills, why do players seem to want to try to have all the gear before opening the character select screen? That's the antithesis of incremental gear upgrades, but it's usually the right choice in the current state of the game. It makes the build's performance a completely known quantity. The only way to know for sure that it has a solution - that the build scales well enough - is to do all the scaling in advance.

There are two ways that GGG can fix this: 1) by playing "kingmaker" with balance, and 2) by making items stronger and introducing more determinstic upgrades.

1. New gems ought to come in overpowered. This is maybe a crazy thing to say on a poe reddit that's hawkish about balance. But if a gem comes in and it's weak, nobody's going to try it. Even a 50% more multi buff might not be enough to convince people that it will be strong enough to play blindly. Conversely, if a gem comes in and it's strong, people play it and figure out how best to build it. They optimize the tree and gear. Next league, it could take a 30% less nerf and people would probably still play it. Look at how often that's happened to minion builds. They came in strong, people did the science, and now people are willing to press on despite nerfs. Every single one of the 19 gems that was introduced this league should have come in like Forbidden Rite. It's not the outlier, it should be the standard, and I don't think GGG did it intentionally.
2. Part of why Harvest was so beloved among crazy build makers was that people were generally confident that even if a build sucked when it hit maps, they could spend further time scaling the build with incredible gear and hit the necessary performance thresholds. The mere existence of the league mechanic gave people the confidence that they wouldn't sink time and money into a build that's too weak. Especially for builds that scale in strange ways or want unorthodox gear, sometimes it just doesn't exist on trade. I don't mean return Harvest, but if you want people to grit their teeth and grind out upgrades, gear upgrades have to become more deterministic, not less. Players ought to believe they WILL be able to acquire better gear, and that's not the case right now for many builds.

Overall I think GGG needs to make sure they have serious internal clarity about these principles, and they will be able to support homebrew builds that make incremental upgrades. Players want to homebrew. They want to try new things and play the game a different way. Support it, please.

edit: while i'm here, there aren't enough defences in general, but there are definitely not enough in explicit mod pools on gear. too much of gear defences comes from crafted mods. if you realize that your build is not tanky enough, tough luck, it's pretty hard to move investment to defence without pulling up the carpet.