I didn't mean to highlight the Tesla X104, but it is the highlight. I got it rolling around Wave 5 or 6, so it even got rid of the Rocket Riders. This means that I could focus on individual threats for the rest of the level. Honestly, I think that the left upgrade is a little OP. It ultimately trivialized the usage of the end of path Barracks.
At least it reduces worry to the wave 1 Necromancer. Him and his random chance of spam-spawning Skeleton Knights. Good luck getting sufficient defenses for that stupidity out at that point.