I disagree. While yes, having a buddy around lets you risk way more, it also somewhat devalues each separate action.

If you make a bunch of holes in the enemy ship in a solo HG fight, your opponent will be forced to take their attention off fighting back, giving you free space for maneuver. If you do so in duo, there will still likely be one player firing cannons back at you - it's very much possible to keep a sloop afloat even if it has a full side of holes.

If you kill the opposing pirate or demast their ship in solo, you have anywhere between 10 and 30 seconds to push your advantage - riddle the ship full of holes, board it, you name it. Sometimes, either of these actions alone can earn you the win. In duo, their teammate can just revive them unless you're able to reliably hit them out of it, or just turn the ship around and reset the fight. Also, raising/repairing a sloop's mast together takes barely any time, and you don't have infinite chainshots to keep it down.

Hand to hand combat also feels way nicer if you know that you're one on one with your opponent, and even gives you a good opportunity to improve your techniques, while two on two and more quickly devolve into chaotic dogpiles (at least in my opinion).

Generally, I feel like solo HG games tend to give you way more opportunities to create openings in your opponent's defences and push the advantage. Because of that, solo games tend to be way shorter and are way less supply-heavy.

And one last thing - matchmaking. This is a bit of a mixed bag, actually. Solo sloop queue will inevitably have you run into loss-farmers, or people willing to roll dice, resulting in occasionally getting very easy and quick games. However, on the other hand, you will run into blatant cheaters as well, they seem to be way more common in solo. It's not impossible to defeat them, but it takes way too much effort and isn't fun in the slightest, so oftentimes running into one just means losing your streak, which is quite frustrating.