I mean... I feel like it got more backlash and was more frowned upon back when the game was new. I remember *childishly!* feeling kind of jealous of time travelers getting all the attention for their towns back in like June 2013, because they were able to make such quick progress compared to those of us who weren't TTing. I admit it was just a silly feeling of jealousy back then, and not a condemnation of the act of TTing, though! But now, the game's been out for years, and everyone's at different points in their towns. Some have started over once or multiple times, others have been playing from the beginning but have taken breaks, others have been playing obsessively the whole time, etc. There's no set "point" that someone *should* be at right this second that makes people who TT ahead have an advantage.
But whether or not you consider it cheating depends on your definition of cheating, and if so, it's certainly cheating-lite, considering it's even an option through Isabelle, and a rumor in the game: "I heard ___'s a time-traveller!" Duping & hacking are probably seen more as cheating these days.
Also, in my case, I use TTing to slow time down rather than speed it up usually xP I keep my town on the same date often because I'm busy pixeling a path or working on arranging flowers or something, it helps me focus on the task at hand rather than worrying about villagers moving or looking for fossils or whatever. I've put 2000+ hours into my game, and still don't have a full-sized tree yet, because I've used TTing to slow time down too much -- tell me how that's cheating