1

Does the level of your bot matter? I got a commanding aggressive ultron sentry at level 22. I'm 55 now and it still never dies, damage is alright.

2

I genuinely don't know! Overall the bot does such little damage that it probably lowers on its damage profile, but in the grand scheme of things probably irrelevant.

Assuming that lower level = less damage from the bot...I'd probably look into upgrading
The Commanding Aura is for you, the aggressive tag is for the bot. So assuming its hitting for less, any max level bot with Commanding will probably outdamage your bot with Aggressive. Finding one of those by cycling Ultron should only take you a few minutes.