Update: You don't actually need Zaraki Kenpachi to defeat espada 2, that was pretty much a big made up pile of crap, sadly.
Anyways i've got Kenpachi myself today and i've compared his stats to my Ikkaku and found out that, Ikakku has more base CRT and has more base HIT, so you do not require Zaraki to kill Espada 2, Ikkaku is fine aswell.
noticed that you need about 200% hit for the 2nd solo fight of espada 2 tower... if you want to regularly hit the guy at least. Which means i need to upgrade my stones a bit more if i want to do it without eagle eyed raider more often then 1 in 10
Group fight is just out of reach currently, think i need to get unohana to give myself a bit more of an advantage as currently i can just about kill the VG before i die