I've found it's actually best to do maximal quality generation and decimate/meshopt to desired budget.
If you're raycasting against your raw art you're doing it wrong anyway, none of the big players do this precisely for the reason you mentioned. And beyond physics meshes, if you're doing anything where performance is a problem you probably want multiple LODs so you have to do this work anyway.
These days you can just ask your agent to build you a LOD pipeline and forget about it rather than sacrificing the art; Claude knows Blender.
Decimating ends up ruining the look of the model to get it down to a game ready size.
Even a simple house model, or humanoid, using Decimate in Blender there is no way that will be even recognizable.
(I agree with you about Blender though, I always hated Blender's simplify)
Some 3D AI providers still leak like that, but Meshy came up with their own binary format that splits the stream up into separate files that are assembled with a response it only gets if you have Premium.
Thought it was cool technology - and wonder if browser games in general are doing stuff like that to protect 3D assets from being easily ripped from the Network tab.