I think they need to balance this a little better, first thing would be not having to use a dozen berries to restore motivation. 1 or 2 ok, but 5, 6? Yeah, lol, no.
My Arcanine is in a gym right now and I had to feed her a berry right away because her 2657 CP went down immediately, now I can't feed her berries cuz her heart is full, yet her CP is not.
If every gym has 6 perm slots and there's only one 'mon in there, I shouldn't have to fight it so much, twice at the most, once to knock down motivation and the second to get it out for realsies.
I got a medal for feeding 10 berries and you were correct, you can use any berry and none are stronger, I wasted a razz to see if that was more motivation than a Nanab berry and the results looked the same.
In any case with Pokestops and gyms being the only way to get berries they need to be a bit more generous with them >