Have you tried updating the controller’s firmware?

I’d rather have better hand grip and ergonomics than small form factor. I used to play on my PSP and DS/3DS all the time, but yeah nowadays the Steam Deck is the best for my hands

Have you tried lowering the resolution and enabling FSR?

Use Luxtorpeda as a compatibility tool and OSRS will run using RuneLite and track time:

https://github.com/luxtorpeda-dev/luxtorpeda