Legendary Ratings

so i've been wanting to make a leviathan and much more legends for quite a while now, but some people are saying that this is a bad choice, because some epics are SOO much better. I've kinda given u on epics (except danshee and whalorn) and i want a full-on legendaries team. Can anyone give me any tips and/or reasons why i should/shouldnt build legends?
Info
Player Level- 29 (like 3/4 the way to 30)
Floor- 5
Monsters Team
SA Bronze Danshee
SC Bronze Cygness
S Arctica
SC Bronze Neon
and building up a whalorn and sneopard

PS if anyone could come and give their ratings on the legends below
Leviathan
Earthling
Fenrir
Peaco
Cain
Hydra

thanks

Fenrir is pretty good.

Earthling is op.

Cain's stats need improvement.

Leviathan needs a better talent.

Hydra is great.

Peaco is op.