Yeah you can't look at Kingery's performance in AAA through any normal developmental or performance lens. This is a guy coming back from a long series of major injuries, including COVID and major surgery. He has only played 96 games - i.e., last season - since returning from all of that. That's not enough games for him to have also fully gotten back on track, nor was he so productive to force his way on the roster, but he did have a decent second half (and his best month was September, .816 OPS).
You have to forget that he's "Scott Kingery" or that he's under contract and just view him like any AAAA minor league invite, i.e., he's Yairo Munoz, with the added advantage of being easily DFA'ed/recalled. If Guthrie and Clemens both stay healthy and are good enough there's no spot for hm, but history says there will always be some opportunities. Had he ended up getting playing time last year he probably wouldn't have been any worse than Munoz, Camargo or even Vierling overall. Maton was better but that probably wasn't gonna last.
I think it's unlikely the Phillies would tender Kingery once they don't pick up the option, but it's definitely interesting that they could.