Consider practical aspects.
All grip switches require long wire runs, compared to panel mounted switches.
The wire runs are subjected to motion, where they transition from airframe to stick. They require special care against wear and breakage.
The grip switches are generally low amp only. That's fine for things like AP disconnect or push to talk, but everything else will require one or more relays, with associated wiring.
Cockpit switches are to be labeled. A coolie hat is pretty obvious, and a trigger is almost always PTT; we might argue that they don't really
need labels. However, given the willy-nilly implementation right here in this thread, you'll need to find panel space for a nice graphic of your grip, with labels for all the rest. In 12 years on this forum, I've seen exactly one (Matt Dralle's RV-8).
Many older guys, in particular those with a bunch of shop time, have problems with basal thumb joints. A whole lot of thumb button motion isn't welcome.
Depending on button arrangement, some stick grips are like a minefield in the cockpit. Buttons on top of the stick are the worst offenders. It's not just disconnecting the autopilot while chasing the cookie bag. I once scared myself silly when the 8A I was flying required hard
forward pressure in the last quarter of a loop. Yes, a trim button had contacted the seat belt latch.
Last consider dynamic factors. One poster made reference to flaps up and down buttons on top of a grip. Ok, so do a go-around. How do you raise the flaps and trim at the same time? Me, I only have one thumb on that hand