How important is proper execution of QTEs in Fractured But Whole?

Solution 1:

You don't have to shit in every toilet, I avoided 95% of them once I realized they were useless.

The QTE in the battle system enhance damage or status effects. You'll do extra damage for hard hitting moves, or inflict extra knockback, heal for more health, freeze enemies for 1 turn longer...etc.

You can certainly beat the game without nailing every single QTE, but they certainly help.

The ones that really matter are the ones with Mosquito who heals because the health gained was valuable I found. They were pretty easy too.

There are even some moves that are just a 1 time button press at the right time. I'd recommend finding the side kicks that have easier moves such as a single correct press or just mashing the X button for 2 seconds to achieve max damage.

The combat is much more focused on strategy than QTE performance, so you should be just fine.