It's the responsibility of the game developer to ensure their game performs well, regardless of engine choice. If they release a UE5 game that suffers from poor performance, that just means they needed to spend more time profiling and optimising their game. UE5 provides a mountain of tooling for this, and developers are free to make engine-side changes as it's all open source.

Of course Epic should be doing what they can to ensure their engine is performant out of the box, but they also need to keep pushing technology forward, which means things may run slower on older hardware. They don't define a game's minspec hardware, the developer does.