I think you’re getting consumed with HOW the game is made rather than WHAT is actually getting made. There are tons of super creative and unique games being made with engines like Unity all the time (or even with Game Maker, for example check out my cousin’s game Fight Knight).
The idea that the constraints of an engine are some big problem is absurd. Constraints are a good thing, they breed creativity. There’s a reason every game jam has a theme and a tight time limit, yet result in some of the most unique game concepts.
I completely agree that constraints can breed creativity—but so can trying to do things a different way than you're used to. If you've only ever made games with very generalized data structures organizing your game logic for you in some predefined way, then PICO-8 can give you the best of both worlds!
There's plenty of games made with Unity and other engines that I enjoy—I'm currently playing a Godot game and it's great.
But if nobody pushes back on the current status quo rhetoric, then many people will a.) continue to have extremely incorrect misconceptions about what necessarily constitutes a “game engine”, and how difficult it is to make one, b.) not be encouraged to try to learn something new that has more general applicability outside of the domain of their preferred tool, and c.) continue to find themselves in situations like Unity developers did last year, or like what some Godot developers are experiencing right now—feeling trapped, with no immediately-viable path forward.
In this past year, I've built my own “engine” that runs a networked open-world game that loads world chunks in and out of memory as players move around the world—but unlike other games like this that I've seen, certain types of NPCs can also freely move around the world, even when there's no players nearby. This was not trivial, but it would've been at least an order of magnitude more difficult, and much less performant (even though I haven't done any optimization work on it yet!) if I was using someone else's engine, shoehorning my approach to solving the problems that this design I wanted to make presents, into said engine's way of doing things—instead of just defining structs and functions that do what I want them to do and writing the whole system myself. It wasn't trivial, but it was MUCH easier than I would've imagined before trying it myself, given that I'm using a library for rendering, and another for network sockets.
So constraints can certainly breed creativity, but if these constraints are left unchallenged for long enough, then you're just limiting your potential for what you can do.
The idea that the constraints of an engine are some big problem is absurd. Constraints are a good thing, they breed creativity. There’s a reason every game jam has a theme and a tight time limit, yet result in some of the most unique game concepts.