I think there's truth in that; there really isn't much mapping from a glider to a big jet in terms of handling, regardless of conditions.
Chesley Sullenberger was a fighter pilot, and a glider pilot, and had a lot of hours in Piper Cubs.... Then later he flew an airliner.
I suspect that in reality, his real strength was the adapability that came from flying a lot of aeroplanes in a lot of different conditions - and simply having done an enormous number of flying hours dealing with an enormous number of "issues" - good and bad. Read his (really very good) autobiography "highest calling" and you'll get the idea. Gliders were doubtless in the mix there somewhere, but I suspect that unreliable and cranky 1960s jet fighters were a bigger player.
Frankly, get passionate for flying, and do lots of flying. What you fly is really a lot less important.
The downside of this is when you realise that being an airline pilot has very little to do with flying, and you'll probably hate it but get trapped by the money.
G