Plummet said..
12knots on a 14m with a 135TT sounds about right to me. i don't think you suck.
As others have said. Get a big board, 145x45 or bigger. Simply swap to your normal board when the wind builds.
Also for light wind loose the fins!. You have to be precise with your edging technique. But once sorted finless is lush and gives you a little more bottom end!
Agree here but lose the fins? What eve's dude. Lot's of LW dudes I know flatten there TT out and rely on the fins to do the work. It all depends on your TT and 138 is not going to cut it for LW. That plus the fact that 14m switchies are well known tug boats and you're walking up the beach dodging green suits before you know it.
Sell the switchie.
Get a Shinn King Gee 150x50 or a naish orbit
145x45 is too small for real LW performance
Also get a 17m Flight - Fatlady - Infinity V3
you'll be in another world of smooth water and easy tricks. Nice