On my f2p account, 5* heroes are rare and mats rarer, except for purple…18 tabards!
So I now have enough to max another less than stellar purple (have C Quintus, Dom and Sartana maxed) with tabards to spare in case I get something better
If you run mono, then the shark would be the best hero to be with your selection. Mok Arr is not ideal on defense because he damages off-colored allies and most defenses consist of rainbow heroes. We did battle in war some Mok-Arr tanks in their unipurple tanked defensive war teams. I advised my members to use mono purple instead and dump tiles to him. Not good on defense but may be stellar on offense. Pair him with costumed Tiburtus and see the very high damage. Add Quint to the mix and those 3 may possibly kill all the enemies on the other side.
Mokky is an attack only hero basically, he is above average for attacking in the right environment. Obakan is below average at everything in any environment.