I think it got a bad rap early on because it's trying to be a jack of all trades. Long range, short range, energy, crit-seeking, plus being fairly quick and jumpy for a 55 ton mech of that era.
All that was paid for with the least armor of any mech that size, which makes it too risky to use it's close-range weapons, thus taking away the versitility it's already paid so dearly for.
MLs and SRMs aren't a bad close range combo. The heat is reasonable, and the "poke holes then sandblast" tactic is widely acknowledged as a being effective.
It's a decent mech once it's modded but I think people tend to shy away from a design that you needs mods from the get-go because it feels like cleaning up someone else's mess rather than customization. Plus the fact that in a lot of scenarios you have to start with the basic model and can't head into the shop for mods untill you're a few battles into the campaign.
Had the Dervish initially been made as a 4/6/4 or a 5/8/0 and devoted that tonnage to armor, it would probably have been one of the most commonly used designs. With the newer tech available, a mech can now sucessfully do what it failed to do in the beginning.
As it stands, it's a design that was either ahead of it's time, or that just tried to do too much.
I still love the crazy thing though. [rockon]