I mean I think there are some overreactions here. Yes his "pitch values" are lower, but thats because of luck not actual drop in skill.
XWOBA (Basically expected stats combining Hitting + Walks)
He is actually the #9 SP this year in terms of XWOBA, guys above include Scherzer, Cole, Strasburg, Sale, Morton, Verlander, Snell, and Ryu. SPs all having pretty great seasons (except for Snell but you know he is going to turn it around too). And out of the Top 40 SPs in XWOBA him and Blake Snell are regarded as the 2 unluckiest.
So in short, this is a buy-low still. After Snell he is the 2nd most big name unlucky SPs and his ratios aren't as bad as Snells are either. His WHIP is still what it was last year and his K and BB rates are as well.
With all that said, I get his slider isn't back but I think that is what prevents him from being a Top 5 SP. He can still be a good Top 10-15 SP. I actually envision him what he did last year, a 3-3.30 ERA, 1.10-1.20 WHIP, and 9k/9 SP. Again, nothing as great as the potential we saw in him few years back. But still a borderline SP1.
Verdict: If you think Snell was a big buy-low, this guy is #2 behind him. He won't be elite without his slider, but he still should be borderline SP1.