I think John Mayer has like 5 of everything. I wouldn't read too much in him using any product.
I don't mind too much who uses what unit in terms of what I myself do.
But appeals to authority -- or popularity, to "the best artists" -- have been a go-to talking point when pointing to supposed "superiority" of A or B. If Andy Sneap calls for an editor, it doesn't matter -- if he uses kemper for amp tones, well, kemper is "much superiorer" to anything else. If Townsend profiles his mesa and isn't too happy with the results, going full-on axe fx, obviously axe fx is just "better than the much inferiorer kemper" to some, too.
That said, if a band uses a given product and is getting tones you like, the unit is probably part of the reason why they are getting a particular tonal end result. Other units could also get relatively similar results, some of the time. There's certainly some causal influence and it may matter -- perhaps a band's usage illustrates just that.
On the other side..take what Christoph said.Even with a KPA2 the current one will continue to get "supported" by all means just like Kemper does with their synths for some two decades now.
Support in what sense though? In the video, he mentions that old profiles done with kemper 1 would sound the same when used in a newer kemper. I am not sure this implies the older kemper will continue being sold or "supported" the same way it is now. Maybe it does; but did he go into such specifics somewhere?