I guess it is -as you said- just you. It is because you said that with more wind the sloops are faster than you.
As Timbo said you need the "turbo" jib in light winds, once you are fully powered (e.g. trapezing) you should be equal or better as uni in upwind conditions . Well, in theory. An uni is more difficult to sail. If you bear away too much the flow around the first sail stalls and you have in case of an uni no power (first sail = main) and in case of a sloop just a bit less power (just the jib(=first sail) stalls, but not the main).
The good news is that you don't need to buy new sail(s) but just a few tell tales and sail more often to learn not stalling the sail.

Cheers,

Klaus