Why would I want phone with worse performance?

Presumably, you had a phone before your current one. If so, you evidently have a preference between slower phone and no phone at all.

Actually I had a desktop computer before my current phone. So my preference is faster, even if it spends more time on the cord.

So get a laptop.

Why though? I find the format annoying.

I use it extensively as a work computer.

It's still better than being slow while being on.

How is a black screen better than a device that's slower, but on?

When my phone battery is low I often can charge it. Most of the time I have opportunity to charge multiple times a day if needed. If I need long life I can switch to battery saver mode; in normal operations I prefer better performance.