The 'Pliers are not a game-breaker by any stretch of the imagination. The Royal Crown coalition was forged when only a few people thought Stanley was a threat. Once word spreads on how powerful Stanley is, others are going to naturally unite against him.

The largest armies in the world don't protect against assassinations. Foolamancy could get a stack in to attack Stanley directly, or kill Wanda in her sleep. Parson isn't the only one to be able to think laterally - Charlie might prove very treacherous. (Mind control spells on garrison guards?)

Vinny has shown, in my opinion, tactical ability similar to Ansom's, if not better. (Vinny could smell the trap that was Parson's very first ploy.) He just didn't have the motivation to use it to lead before. He might, now.

The 'Pliers will certainly make raising and maintaining a large army easier. But the bigger the target, the more weak points it has. They might not be able to take Gobwin Knob, but containment works just as well, and the more area they take, the more they have to defend, and the more spread-out they get.