I must be forgetting some people, but I'm not sure there's a ton of great comps for a Cueto-in-the-AL type situation, ie, a high-level NL pitcher making a mid-career transition to the AL. The only one I can think of off the top of my head is Mark Buehrle, but he's kind of a unique guy and I'm not sure he's a great comp for anybody. Plus he pitched in the AL for a while. I guess there's Jake Peavy. He kind of struggled in moving to the AL, but that also coincided with him being hurt a bunch. Nolasco, too. Ervin Santana had a spike in his K% in Atlanta that mostly went away when he went back to the AL, but he'd had rates that high earlier in his AL career. Eovaldi wasn't all that different from the guy he was in Miami. His BB% did go up a bit, but his FIP- went down so maybe he got a little better? Wandy Rodriguez sort of fits, but he's been hurt so much it's hard to know what's going on with him.
Oh wait! Hamels! He might be the best comp for Cueto other than Cueto himself. Hamels was more or less the same guy in the AL as the NL. He struck out batters at a lower rate in Texas but nothing too out of line with what he'd done previously in the NL. Gallardo struck out fewer too, but his ERA wasn't all that different. Cueto himself wasn't all that great in his brief AL time obviously.
So, hard to say, I guess. Intuitively you would think it would be harder to pitch in the AL because of the DH, obviously, and the AL does tend to win more interleague games, so it may just be the superior league as well. That could be partly because it has better pitching than than the NL, not necessarily better hitting, although I would bet that AL hitters are just better overall, even if you compare them to only NL non-pitchers. Although maybe not. It's a tough comparison to make statistically.