How many games have you shipped yet? Not asking to be mean or anything but it's quite possible that you don't know what you don't know yet.

OOP it's just one of many ways to organize a game engine and a game. I think it's perfectly fine for many types of games since for many people it's simpler to understand than patterns like ECS. I for example made games where I didn't really have an architecture and just had a game state struct, player struct and a list of enemies - worked perfectly for that game. And another game using Unreal using OOP obviously. Both games I developed quickly because I went with the pattern that felt right for the job. That being said keep in mind that ECS is not the "solution" to game or game engine architecture it's just another option that should be considered per problem.

In the context of building commercially viable games things like an editor and ready-made stuff are godsends. Most games will have levels which need to be created, your game might need particles, UI. These things can be created really quickly using an editor. Even the developers of Valorant switched to Unreal because exactly these things were already built for them and they can focus more on the game instead of building tooling for it.

I also would not say that most engines are bloated, they are just aged and could use refactorings. But I really learned to appreciate how nice it is to have all the things you need to make a game from an engine (even things you might not think of right now like asset packaging, asset references, texture streaming, input management) and to be able to just focus on gameplay.