Oh, I know he's not going to kill anyone but the fact that he can even take the whole team on his own is rather abused, even with advance weaponry. Cable may have been able to take down 3 Avengers but the had future tech, the element of surprise, and his super powers.
Plus, what contrive reason would he have to attack the Avengers?
Well Frank has displayed the ability to contend with all but the toughest of superhumans from time to time in the past mainly through planning, preparationj, ingenuity and toughness.
Certainly hes had the better of a number of more 'street level' heroes on numerous occasions including Cap, Spidey, Wolverine and Daredevil, so I doubt that the likes of Cage, Iron Fist, Dr Strange, Black Widow or Mockingbird would really be beyond him even without some tech to back him up. With a little help I doubt theres much thats beyond his ability.
As for the 'why', the only reason I can imagine Frank going after the Avengers is if he genuinely thought they had become a menace - a distinct possibility depending how AvX pans out and it wouldnt suprise me if Wonderman wasnt the only person who believes the Avengers have caused more trouble than theyve solved.