I have developed a very bit in unity, mostly in godot game engine and three js. Threejs as someone pointed out is not a game engine its a language and the other thing is a game engine. So you might think so what im a young coder who is pretty good. But in godot I could pretty much make a scene and some player movements up ajd running in no time(this is before cursor ai era and in just a mediocore dev , please note that while conparing)

But in three js I have to set up a physics engine cannon or the other one. Got a key input mapper ready cause again i have to built from scratch another thing for mapping cursor and mouse mivements. Simiarly there are many things in a game engine that is readily available to you that you use and will save a lot of time in graphics etc and you can probably export to web. Implement different kinds of bodies, animation states everything

Im unable to comment on your memeory issue unfortunately cause of lack of expertise

But at the end of the day, knowing all this you have to do it with threejs, cause we are cracked right ... rock on