First of all, I totally agree with you.
There should have been more gay characters.
and secondly, I did not like how homosexuality was portrayed in the series.
Specially when Piper told Leo that Phoebe was "supposedly" a lesbian.
And yeah, concerning Brenda and Carly.
Brenda was also among the few innocent people the charmed ones failed to save.
How ironical is that!
I still like the show, but I also thought that it was a bit racist too.
I don't remember seeing mixed couples.
Not only there was only one lesbian couple, that ended up tragically, but I don't remember black and white couples...
It was always either black/black or white/white.
But this is just me, and my opinion.
I may be wrong.