Techmarine is looking to be a fucking failure of a class that they had no clue how to implement.
Seems all of kit is built around his dogshit sentry turret that either spawns in a spot where it doesn't even have a line on the enemy, or it spawns in after you've cleared the wave and don't need it. The fact it dies so quickly doesn't help. If it were an equipment piece you could carry around and deploy that was on a massive cooldown, sure maybe. As is, it's worthless.
His servo gun is just inconsistent. It's got too long of a cool down and it doesn't aim for the head, so anything other than plasma is wasted ammo. It's main use is letting you do gun strikes without doing the animation, but you still need to pull the trigger. I can't remember if there was a perk that made this automatic, but if not there needs to be. Along with a cool down reduction.
His weapon selection is kinda dumb. I don't think he should have any primary ranged weapons. Whatever big guns he has should be for the servo arms, while he carries a melee and sidearm. He also shouldn't have the combat knife and should have the thunder hammer instead because it actually works with some of his perks unlike the knife. Besides a knife on a Techmarine is fucking stupid when you've decided to build to class as a crowd controlling murder bot. The knife is the worst weapon for that.
They really should have done an Apothecary. Make it a Biologis so we get another Gravis unit, and he could have given damage buffs to the team against nids and the chaos spawn/beastmen, with maybe a few perks that promoted better armor or health regen, starting the mission with a couple stims, big bonus for reviving etc. But Saber thinks any sort of healing outside of Bladeguard and Vanguard would completely and irreversibly break the game the same way letting bots make use of team perks would, apparently.