I also don’t think there is anything wrong with filtering extremely old nodes at the discretion of the operators - but it’s weird and probably a bug if a DNS seed wouldn’t ever return nodes with a current and widely used version, which was the case in the linked issue (and quickly fixed).
In my opinion, the most important benefit of gathering this kind of statistics isn’t so much evaluating / comparing the quality of individual seeds, but to hopefully make it visible if something abruptly changed in one or more of those - that could be a sign that this seed got compromised.