TL;DR they are comparable.The Megas aren't really comparable from a competitive perspective. Their viability is dependent on the format you're playing and they have completely different roles; one is a dangerous sweeper (Singles and maybe Doubles?) while the other is a powerful Wallbreaker (Singles) or Spread attacker (Doubles). Because of this the general opinion of which one is the "better" one is based on the format. Not dissing your opinion or anything, just thought that needed to be said.
They are comparable, they don't fill the same role on a team, but they are definitely comparable. From a competitive standpoint, they can not be compared in the same role (who is the better sweeper for example) but they are comparable in general. They does not fit on the same team-structure, but it is definitely possible to compare them in categories such as team support, momentum cost, usefulness against the most commonly used pokemon, checks, counters etc. etc. In singles, if every team caries 2-3 pokemon that could take advantage of Zard X (or visa versa) while Zard Y gets a free kill every time it comes in, you could definitely say Y is better. In doubles, is every team had flash fire abusers, while being very weak to physical dragon moves, you could say Zard X was better there. On a side note, I don't think Pikachu315111 was even trying to compare them from a competitive stand point.