Look, I'm not calling Ajani himself amazing. He's certainly not even close to Sun's Champion. That said, the "does/doesn't protect itself/doesn't protect itself against multiple threats" thing, while not invalid, is really overdone and falls into the same trap R&D seems to have where the only "real" and "fun" Magic is aggro to midrange with minimal answers where spending your turn on a 6 drop means eating 4+ face damage from attackers. In a Standard meta where Ajani would sit around and do his thing for 2+ turns he very much will win games given his +2 is one of the, if not the actual, best repeatable card advantage abilities ever on a planeswalker.
Yes, Ajani is entirely unplayable in anything resembling current Standard because you activate him once and then he (or you) get plastered by vehicles or 8 billion Cat Beast tokens or, less often, a bunch of creatures with at least four +1/+1 counters on them. Control and/or more durdly decks just don't exist and those are the only decks Ajani can remotely function in. And yes, given the direction Standard has been going recently it's hard to see this changing before he rotates out of the format. As my original comment said, there's a meta where he could potential put in real work but we sure as hell aren't in the same universe as that meta right now.
