It's a slugger in an environment where most opponents are snipers, and there's rarely any cover to protect you on the way in. The fore-and-aft nature of the main guns exacerbates this, as an undisciplined player who turns to bring those guns to bear before closing to at least medium range stands a good chance of suffering severe crits before getting any good shots off. That said, if it can get close in a condition to get accurate shots with those main guns, it'll do horrific damage to anything smaller than a cruiser.
Whirlwinds aren't bad per se, but they're like taking a Hunchback onto an open map - your odds aren't good, but if your tactics work out, you'll be rewarded with big boom.