Depends on the game mode with Mino's:
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Coop : If you play against the AI, you just build an army and win. The advantage of AIs is that Minotaurs with half HP usually go back to repair.
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Team: If you play small teams, no one builds a Newton because it does 0 damage, but rather a Drag-Turret is because you can easily destroy it with cheap raiders.
And when you play big teams there are enough crazy players who spam Impaler that makes a short noise and death is the Newton.
And Jack I don't know about is actually just a support unit because already raiders with increased range can destroy them easily (for example : Pyro)
The only thing I personally find Newton good for are Lihkos, best just dig in so that the pilot does not see this at first view :P