Trap started with throwing glass balls to simulate flushed birds over a dog. Then they developed the clay target.
Geez! I guess I will date myself - in the 80 s I always used a 26" barrel with skeet choke (no tubes) in both 20 ga and 12 ga for pure skeet, and a 30" full choke barrel for trap. I thought any weight advantage you could get was the way to go for skeet. Since I have never shot sporting clays (which I guess combine skeet and trap), I cannot really comment on what is best; guess it all depends on what kind of hunting one does - may need the versatility of a mid-length Harrell for mixed, but I found the shorter barrel good for pass-shooting, particularly ducks.
This is just my opinion but, for me, a 26" O/U is too short for any game or any quarry. I'm not saying it won't work. I'm not saying you can't hit with it. I'm just saying it's not the best tool for the job. Even for the "quickest" shooting I do (grouse & woodcock) I've found a 28" O/U works better.
Yes, there are hundreds of thousands of 26" O/U out there in the world. Yes, your Uncle Clem won the club championship with one. No, the clay doesn't know what barrel length broke it. (As an aside, the clay is in animate so it doesn't know anything)
IMHO a 26" double is best suited to a shooter of small stature or one who is looking for a bargain (since 28" is the minimum length that a large segment of shotgunners will consider). I like 30" barrels for skeet and 32's for clays, with 2" +/- not a serious handicap.
(As an aside, the clay is an inanimate so it doesn't know anything)
Since I have never shot sporting clays (which I guess combine skeet and trap),