Ethics aren't different if you're on a 5.12 or a 5.2 ... the only thing different are the egos or lack of humility involved. So yeah, bad on them for leaving it there, no matter who or what.
more people want to climb easier routes. that makes it different, because the chances of someone else's ascent being buggered by gear on a 5.12 at the notoriously-'sandbagged' gunks seems a lot less likely than on a 5.6.
that being said, the gear was up for far less than the 24 hour "booty" "rule", more like less than 12 hours. it was still there when the OP was walking out a 7 because we were still climbing at 7, and camhead was gonna take one more run on KC.
In reality the Gunks aren't that sandbagged, and you'd be surprised how many people are climbing 5.12 trad, both Gunks resident climbers and those that are travelling. I just say that since it happens to me at my home crag all the time. And when I'm travelling to the Gunks, I'm usually out on business and I usually only have a day and to mess with other peoples gear is a PITA,....