If I tie my two centrelines together I get a loop that's shorter than either 🤣
I know what you mean though, sometimes you need to add an extension, I just got annoyed with doing so too often and fitted much longer lines.
It also matters where you do your boating of course - if most locks you use are only a 5 or 6 foot rise you probably won't benefit from very long lines. If most locks you do are 10 or 12 foot rise, you need them to be longer.
My usual (crewed) broad lock procedure is centreline up, passed behind a bollard and back down to the steerer. Works well in all but the deepest locks, and saves a lot of revving.