I just wanted to address this bit first. Chansey does have to options available to it that render Fake Tears / Metal Sound mostly useless. CM Chansey isn't used as much, but it is out there, and can hit pretty damn hard if given the opportunity.
I don't see how "most" of the physical walls paired have instant recovery not highly supported by wish. I see this as true when paired with Slowbro or Vaporeon (if wish/protect counts as instant recovery), But Skarm is stuck with rest which makes it setup bait or switch bait, and Weezing has pain split, which again, just doesn't compare to Recover/SlackOff/Synth. Pain Split is only as good as it is because of Wish Support, otherwise it would be very prone to wear and tear.
The differences are very apparent between P2 and Chansey, I am not sure why you are not acknowledging them. The ability to switch out of status, more or less for free, is a pretty big deal on a wall. The ability to Wish pass is kind of a big deal, but not quite as much. The ability to scout CBers is kind of a big deal. The ability to run a cleric set is kind of a big deal. I am not exactly sure how they are not different.