A bunch of the fellas I fish with in BC do that very thing ... too old & stubborn to try to change, but relaize the advantages of casting / mending with a super long rod. Actually some of them fish overhand in the truest sense, a couple of others cast more with their hands low but without a spey cast of any type.

I have a hybrid 11.5 footer that I love to fish up there. can be fished either way, but I usually fish it as a single-hander.

Slow is the key from the experience with my rod and watching the old farts with their "spey rods".