I don't expect or want him to play solos like he did back on the early albums, quite the opposite (that goes for all of Metallica too). I actually want him to play something that fits his current level of ability, and it sounds like the leads on Hardwired to Self Destruct are doing that a bit better.
I just have the basic expectation that a musician of his experience could at least manage to play a solo that was in time and in key, or musical in any way, shape, or form. Instead the solos on DM sound like any 12 year old kid on Youtube who's just learned to badly play the MoP solo with his fudgy little fingers on that guitar that's too big for him. I just want Kirk to slow down and pay attention to note choice and timing, instead of fumbling over the fretboard to fill time.
tl;dr - I'm criticizing him because he sucks, not because he can't play the way he used to.