You are completely ignoring the fact that it's Larian's design choices that have made Sin Tee's solo runs possible. The fact that he is stacking all of them to accomplish the feat, has no bearing on the fact that it's Larian's decisions to deviate from the rules so sharply that his exploitations are even possible.
Sin Tee can't pull off what he does in those videos if Larian doesn't homebrew their own 5E rules and slap them on top of the DOS environmental/barrel/surface spam framework, and instead stays closer to 5E rules.
Firstly, my whole point was that solo-combat is a fringe method of gameplay and really isn't the best way to evaluate what works and what doesn't in BG3.
Now regarding Sin Tee and soloing - Larian's design choices are merely the current method he's employed to solo this game.
It's impossible to prove that the game is not solo-able without this - but I'd put my money on him being able to do it. Especially considering that a closer adherence to the 5E Table Top will simply bring in half a decade of even better thought out cheese from the table top community. 5E is simply too ripe with explolits (i.e. people have come up with ways to solo a 30 CR Tiamat with a level 4 character)
As long as the game offers significant freedom, and there is no DM intervention to moderate meta-gaming, players will likely find a way to solo a single player D&D game. Even PF:KM unfair and IWD2 Heart of Winter Mode, where monster statistics are monstrously skewed, are solo-able.
