First of all,
John is terrible. Compare him to
Oscar,
Oscar has +4 manipulation. Compare him to
Jiro.
Jiro is 7/4 against SOA and
John is 5/4. This character is below average for competitive
ELO.
Coby is is a great character but his huge vulnerability to SOA keeps him from being a top
ELO 4*.
Coby gives your opponent the option of using a SOA character for -4 damage. This is a serious drawback.
I think
Martha is ok.
So going mono with Sentinels only really gets you a great but not top 4* and a decent 3*. When I factor in that Sentinels is one of the more shallow clans in
ELO, I find that they are a better half clan than mono clan. You should pair
Jakson and
Lehane with a clan that has a more consistent 4* than
Coby, a more powerful 3* than
Martha, and better DR characters than
Melvin and
Morgan.