Porygon-z already serves the role that you're trying to push kommo-o in as a wincon when you get rid of it's counters.
Also while kommo-o has the better bulk statwise, porygon-z has the better practical bulk in that it's weaknesses are much harder to exploit and it has access to recover moves.
Also there's the fact that kommo-o, at +1, does not hit NEARLY hard enough to discourage naturally bulky pokemon from switching in because in the end, he still has at best a 110 base attack stat and his speed is low enough that even with a boost he can't justify using a non speed boosting nature.
and yeh, he attacks when getting the +1, but how much does that matter really? It's a move with a typing a large number of very high tier pokemon are immune to allowing them to block the damage, and which can then retaliate with a 4x SE attack which, as demonstrated can still destroy kommo-o even with the boosted defenses while it fails to ohko in return thanks to it's mediocre attack stats.
Remember that kommo-o already has dragon dance and it does nothing to help him. >The fuck are you on about
they actually did tests on it, Boomburst porygon-z would be so ridiculously powerful it puts him at the very edge of ubers