You think the only game you will lose are generic Unity shovelwares when in reality you will also lose good games made by people with good sense in game making but likely not the resources or technical expertise to make their own engines. Think Cities Skylines (Unity, the studio had only a dozen people in total when it released), Dusk (Unity), Undertale (GameMaker), Spelunky (GameMaker)..

Another comparison is game modding which is essentially using the base game as the engine of your modded game. Do you think Team Fortress or Counter Strike or DOTA would have been made if their creators thought they have to build their own game engine?

Lowering the friction to make a game means more games get made. Yes there will be a flood of bad ones, but we get good one too.

Survivorship bias. Most games are indie games. Indie game devs who deside do use custom engine don't make it to sales.

I don't think the engine has much to do with the creativity or originality of a game.

If anything, not having to build an engine frees up more time to get creative with the actual game.

Most games are bad, of course, but Sturgeon's Law applies.