There are many great things about an all-frag build, chiefly that it is fun, it offers the possibility of a quick victory not a long drawn out grind-fest, and that it gives the user a clear, defined tactic to pursue.
The reason I don't use them anymore (and I have used them as much as anyone) is that the all-frag build runs contrary to what I generally consider the guiding principle of PvP outfitting, as outlined on these forums long ago by dread pirate Cmdr Derath, in the early stages of ED, when he was perhaps the galaxy's most celebrated PvP-er, with his Cr.100,000,000 bounty. I paraphrase slightly but the maxim is essentially:
"Build to beat the best ... and you will beat the rest anyway."
The all-frag build is the direct opposite of that, 1v1. If you beat someone with it, they weren't the best. And you probably would have beat them with something else anyway. And if you do meet the best, you won't beat them.
Still, enormous fun though, which after all is the point of playing a game. And as others have said, surprise attack in winged combat is a different ball-game: there it can (sometimes) beat the best.