Once again you're trying to make something major out of very little. Yes, Devin needs to cut down on his turnovers a little. But you should take a look at the leaders for turnovers per game.
Devin is averaging 3.91 turnovers per game, it would be nice if he could cut that down to around 3 per but that is hardly the big deal you make it out to be. Harden averages over 5 per game and Trae Young, Westbrook, Doncic and then Booker round out the top 5 and just behind Devin is Ben Simmons, Giannis, Lebron, Drummond, Bradley Beal, Paul George, Lavine, Kawhi, Embiid, Morant, Jrue Holiday and Julius Randle. That's pretty good company.
And in what way is his defense "regressing again"? And, "regressing again", makes me want to ask you when his defense regressed prior to this but I'm afraid you'll pull out a video of him in 3rd grade. Anyway, to me he looks like one of the better Suns defenders out there most nights, not great but above average usually. On a team minus a defensive anchor, I don't know how you could expect much more than that from your scoring guard.