Happens semi-often whenever a thread for either game is up, normally along the lines of "Horizon/Zelda is alright, but insert not-so-subtle way that I think Horizon/Zelda does X better".
There was even a thread that directly compared the two awhile back. I wouldn't really say its a blood-war, but a rivalry of sorts is definitely present lol
Nah, I am excited for Zelda, whereas I am "wait and see" for Horizon. In general, I've always found it annoying when people randomly put down another game in order to praise another in a thread that never called for it. Just pointed out those two specific games because they're the most prominent examples at the moment, as the comparisons are going to be made due to their proximity to one another(and other stuff I guess...) , for better or for worse. I just find it amusing when you got people all hyped in the Horizon thread, and then suddenly someone talks about how much it looks better than Zelda. And then vice-versa for the Zelda threads. Like I'm more interested in Zelda myself, but I ain't gonna go and gush all about it in a Horizon thread. It reeks of insecurity to me in a way when people do that, but meh, whatever.
As for responding to them, I rarely do that, because I don't want to be the one to help derail the thread. And as far as ignore lists go, I don't pay enough attention to notice if it's the same culprit(s) to bother considering such a thing. Even if it was, I wouldn't, because in the end it's just a minor annoyance, not something I would be disgusted to read or so.