Honestly, I always played defensively and let them come to me if BB4+, used my range advantage against BB3-, and only rushed in when they were blind or distracted. The same thing you do with a BB2-3.
If you want more: the thing with the Monty is that, like they said, it hits like a sledgehammer. And what's more: everyone knows this. Even if the enemy is not giving you a shot on them, you can still prevent them from gaining in the battle. Simply inch towards them slowly (as in just slightly angled from vertical) or feint a sudden rush by turing in and turning back quickly, and better than 9 times out of 10, any BB will retreat. A single Monty can easily keep 4-5 BB4+ at bay by just scaring them back. In GB, a coordinated rush is highly unusual, and that's the only way they'd go in.
If you keep that up long enough, the battle will grind down, and one of two things will happen:
-1) Your team will be losing, and the enemy will start to get more aggressive. You can get massive attack as they try and rush you, netting solid experience even in a loss. Just know your angles and keep aware of where they are. Again, they almost always come piecemeal (as fast as they can) rather than coordinating.
-2) Your team will be winning, and the enemy will be starting to focus on where their line has collapsed, often giving you a chance to get in and get some hits in.