I've played Eeth Koth from 3 stars to 7 stars since about day 1. (Yoda can go F himself.)
He is awesome if you are running Jedis. His potency is okay, so his stun lands a lot and his speed means he'll come up again quickly enough that you don't feel like it's always on cooldown. His damage is more than acceptable, game designers are not generally going to make somebody with amazing damage and a stun.
He won't help you with Sidious. Well, on paper he might, but if you need the Stun (or damage) to land, you can be sure Sidious will deflect. Also, I don't think there's any non-Jedi that can one-shot Sidious when paired with Jedi/Jedi leaders, but I'm not maxed out.
You were asking about his max stats, have you never been to SWGOH Cantina? Note the links at the top.
http://www.swgohcantina.com/character-max-stats/
What on the surface sucks about Eeth Koth is his lame anti-Droid abilities. I have him at 4/4/1/1 because the extra anti-droid stuff makes me pass him by.
Which sounds crummy...but honestly it just saves you Ability Materials to spend on other characters. Assuming that you don't have an unlimited supply of purples/3's this actually makes you stronger since the team as a whole benefits.