Interesting. Some will tell you that PETG is the new ABS. Having a little experience with it, I can see why.
But warp tendencies with PETG are somewhat all over the map is seems. I have clear that doesn't warp! I know that's a bold statement, but then I try the Amazon black PETG and it is as bad if not worse than my ABS. I can only attribute this to colorizing pellets being more like ABS rather than the nature of clear PETG. But this is a lot of speculation.

I don't have a heated bed so managing ABS can be tricky but I've learned a few tricks over time. If I keep the room at 70F or better, it seems to do okay. I will also pre-warm my aluminum build plate on the stove. Nothing drastic, just warmed up enough to take off the first layer thermal shock. My plate's magnets don't like high temps!