I have killed most of my rifle shot deer with a .450 bushmaster - and it has hammered them. But, I have never shot one over 100 yards. A lot of folks here did exactly as you said - including me. I bought a .350 legend package gun for my grand daughters to use instead of a ML. It shocked me when I opened my first box of .350 and saw how small the cartridges were - compared to my .450. A lot of the guys here did cripple a lot of deer with a .350. They advertise that round is good out to 200 yards. I am sure it will kill a deer at that range, but I wouldnt shoot one over 100 yards. I think the .400 legend a lot better round.Casual anecdote time.
My state began to allow straight walled cartridge rifles a few years ago in both the "muzzleloader" season and also the general firearms season in a region of the state (Michigan's southern lower peninsula, where 60% of hunting effort is applied and 75% of the deer herd resides) where it was previously a shotgun-only zone.
I have noted an uptick in the number of dead deer carcasses on my farm, obviously wounded from nearby hunters before running off to the best piece of cover in the township to die. I find 5-7 each year, usually all bucks, in an area that is overrun with does. Disturbing.
I think guys plunk down their cash, buy their rifle with a shiny new chinese scope already attached to it, get her boresighted at Cabela's, watch a few videos of guys killing big game at extended distances, and can't resist touching off a round or two at a deer 300 yards away just as legal shooting light expires. I am certain this is going on around me.
I did shoot a deer with the .350 during mg season. Quartering away at 60 yards. Entered second to last rib and exited through the meat on back of off shoulder. 180 gr win. It didnt go far. But I dont doubt what you are seeing.
And as you say, anecdotal evidence, among our hunters - crossbow, compound, ml, mg - I have seen more deer lost with a 6.5 creedmoor than all others put together. And no, we shoot more with archery equipment than anything else. On paper, the 6.5 should be great - for us, it has not been.