The Nintendo Switch uses a mobile chip as well. There’s not really any reason to believe that Epic is having trouble supporting the game on ARM.

I don't think running game on iPhone is problem, but Nintendo Switch (or say gaming console) might have better cooling design compared to smartphone.

No "might" there - the switch has a heatsink + fan(s), sizable vents and probably a much larger battery (when portable, unlimited power supply when docked). The Switch works with a much larger power budget compare to the iPhone - input and output.

Nintendo Switch is a gaming device featuring a 720p display. An iPad is a general purpose feature with 4x the pixel resolution.

Games generally don't render at native resolution on phones.

Does that really matter though if they have 100,000,000+ downloads on iOS? It would make sense to just do whatever you can to work around performance issues when it brings in the amount of money it does.

Anecdotally, I haven’t found that to be the case on the A10 through A12 chips. I’m impressed with Epic’s engineering.