Your sentinell WILL get stuck between your repairing GMs and die quite a few times. It sounds good on paper but in practice it's a living hell to control to its full potential due to the game engine's pathfinding hating you with a passion, so controling the sentinel and having it do what you want it to do is a skill of its own that should be your priority to learn. It's also a kiting beast with how it can shoot while moving backwards.
Since code-wise it's only one single gun, all that damage gets focused on one model most of the time contrary to your GMs which even though have more dps with serg, the damage spreads out quite a bit. You can use it to slowly peel health or even models off an opponent that likes to hunker down before he can get enough firepower to kill it past your GM repair support. The sentinel will be the absolute core of your opening engagements.