Easy, just ship iPhone 18 Pros to all of your users

Devs should be provided with shitty hardware, such that their code will run smooth on low end devices and insanely fast on high end.

Surprised there aren't simulators for this like there is for slow/spotty internet.

surely there are? can you not run like an iPhone SE in Xcode?

sure you can but its not simulating literal iPhone SE hardware, the software goes as fast as the Mac can run it. which is more or less midrange iPhone speed although wildly different limiting factors