This certainly did happen often in XI, and for as long as I played that people always seemed to be intent on saying, "I'm getting 200/kill this is good (our kills might be taking 45~60 secs each)." instead of, "I'm getting 120/kill but just hit chain 68(means an avg. kill speed of <10secs)". People are hard to convince even when presented simple math, once that idea is lodged in there it can take a number of blows from a sledge hammer or 20 to finally get it across.
In XI this trend started to change in older players with a few jobs that were 70+. Course Abyssea broke all the rules for XI xp parties. My hope is that it'll change here too.

I should also say that I've been known to want to step it up, usually when kills are happening in <5 secs avg and healers are doing nothing but holding onto their sticks. If you step mob level up 3~5 at that point and the party fails maybe it was really just a shitty party to begin with but because of the relative ease of the mobs you were originally fighting it seemed good.