Well a lot of this really depends on the source material. The L2 is a classic and can be heard on a ton of records out there, but it does not sound good on all material or if not used properly. The L2 gives off some artifacts when pushed and this could be what you are hearing. Again, depending on the material it can make it sound like crap. It would be safe to say that the compressor that comes with FL also gives off it's own sound when pushed as I don't believe either are very transparent like less say the Oxford.
Anyway, I have heard this before that the plugins that come with FL sound better than Waves. I have never done a shootout comparing the two, but it does not seem likely to me. I think if Image Line were able to create plugins with Synth Edit or Synth Maker (can't remember which one they make most of their plugins with) that could be in competition with Waves, it seems that they would create some bundles and start selling them as VST's and RTA's. Even not selling them for half of what Wave Bundles go for you are leaving a lot of money on the table. Now I would agree that the L2 is over priced, like almost all Waves stuff, but I am not sure my FL compressor is on par with my L2. You want to also keep in mind you are comparing a compressor with a limiter and they work differently. The limiter is not working with the whole sound and of course cutting of the sounds above the threshold, in turn the FL compressor is pushing that sound which may sound better with the material you are running through them giving the impression that the compressor sounds better when in fact you just can not hear that part of the sound anymore because the limiter has cut it out.