If you are looking for a general purpose champion, I would definitely go with Apothecary. He is very usefull in all potion keeps, dungeons, doomtower and early game clan boss.

Geomancer for Clanboss. He has to be lvl 60 and Giantslayer mastery skilled. When the Clanboss attacks your team while under a HP-burn placed from Geomancer, the Dwarf will hit back with his passive. Each hit from Geomancer's passive counts as hit for Giantslayer.

Your arena team needs a rework in general. You have no speedbuffer and no speedaura, so your team will go second. I don't see anything in your team to survive this. You just get def-debuffed and killed on turn 1, before any of your champs can act. 

Either you rebuild your team completely to something like High Khatun, Apo, Warmaiden, Athel, or you put in Apo or High Khatun instead of Rector Drath and make the speed-champ and Martyr fast, so Martyr can activate her counterattack + def debuff before you get hit.