I agree with you. I like fatter strings on single coils for that fat strat/SRV tone, but it doesn't really work on humbuckers the same way. With Mules you can pull off 11s or 12s at standard tuning without a problem, but on say a Miracle Man, the lower frequencies will be overpowering.
I find I can pull off 9s with high powered pickups and they usually sound smoother, where with moderate or lower output, I will go no lower than 10s.
I have experience with this on my Jem (Evolutions, high powered ceramics)... 10s had more lows and highs and 9s were smoother, and on my Les Paul Classic when I had stock and Duncan Distortions in it for a while (went back to stock eventually, found them a lot better). I tried some 12s and 13s and even 11s and they were just a mubucket but it was usable with 10s at least, and I can't stand how 9s feel on a Les Paul but they may have worked better.