He has just shy of twice the takeaways as he does turnovers. He has 26 giveaways, which is tied for 149th most in the NHL. He's no more careless with the puck than any other forward who is playing big minutes in an offensive role.
Here are some notably forwards with 30+ giveaways: Ovie, Eichel, Larkin, Kadri, Dubois, P Kane, Stamkos, Svechnikov, Huberdeau, Necas, Keller, Aho, Koptiar, Kuznetzov, Toews, Zibanejad, Crosby, Tavares, Robertson, Meier, Matthews, Trocheck, M Tkachuk, Marchand, J Hughes, Panarin, McDavid, Panarin, Marner, Kucheron, Draisaitl, Barzal, Malkin. and Pastrnak.
He's on pace for another 20 goal and 70+ point season despite not having much of an answer for the adjustments teams have made to him. The vast majority of 1Cs don't meet the criteria you seem to be placing on him and the ones who do are worth a hell of a lot more than the contract Thomas got. Guys pushing to point per game take chances with the puck. That is the reality of the NHL.