If you’re playing FFX/X-2 on PC, consider installing the Untitled Project X mod. It fixes some stuff and adds more graphics/UI options, but one of the most significant changes is that it allows you to toggle exp to the whole party regardless of participation.

It completely eliminates the “swap every character in to guard for 1 turn” hassle. You basically never need to grind, because every single character stays properly leveled. Basically, the game difficulty was balanced as if you fully utilized every single character in every fight. So the mod allows your exp gains to reflect that expectation, without needing to mindlessly swap each character out every time.