>>58137575 (OP)
I always had this theory-ish kinda headcanon as to why you wear your gimmick items where.
You wear the Mega Keystone and the Dynamax Band on your right arm as a symbol of "power". Mega Evolutions allow a Pokemon to transcend their limits into a new form, and Dynamax is essentially a semi-physical aura made manifest.
You wear the Z-Ring and wield the Tera Orb with your left hand as a symbol of "potential". Z-Moves draw out the potential for a Pokemon's abilities to their limit, and Terastal awakens in all Pokemon, and can be changed to any type to maximize their potential.
Not to say the Omni Ring's bad, but it is nice we have a canon all-in-one machine. (I think that gold band inside cuff is a selector dial personally.)