If your alliance uses purple for tanking in wars, then maintain your Ursena and place her to at least +19. She is by far your best purple tank since you cannot allocate paladin emblems to Clarissa by reason that they are with your Odin. Alfrike would be a good purple tank but only in very fast wars.
But if your alliance is lenient enough to allow its players to have their war tanks to be of a different element which has a hero ideal serving as tank (even though it is not ideal) then by all means, change your tank. So far, a fully emblemed Garnet or Black Knight flanked to the left by a highly or fully emblemed Frigg and flanked to the right by a highly or fully emblemed costumed Kadilen or Odin. At the wings are heroes punishing enough like Cobalt/Finley and Killhare/Onyx/Jabbawock. Some players tend to have Garnet tanking taking advantage of the ninja family bonus (chance of dodging specials and tiles/regular attack as well as minor counterattack) when accompanied by Cobalt and Onyx at the wings and flanked by Frigg and costumed Kadilen/Odin. That is the emerging meta in its attempt to replace the former ideal GTV defense core. You need to put this into consideration and perspective.
As for Krampus, we rarely see them on raid defense on the upper diamond tier maybe because Krampus is still relatively new, or that not so many players have already maxed him if they happen to snag him from this xmas portal, or that players are still testing other heroes ideally best accompanied by Krampus and check their defensive synergy. So far, I don’t have any apprehension of him tanking or any other blue heroes for that matter. My main monogreen team is vegan enough to defeat them. Who knows, maybe in a month or two, we may be seeing a full switch of the current meta.
At any rate, your roster is still young. You need to have more heroes maxed and emblems to activate talents. Expand your heroes by getting more and leveling the ideal ones. You can’t really compete with the most elite players with all their prized heroes and troops in their possession and emblems obtained from all sources. There is still no war or raid defense hero setup too strong to be insurmountable by the pesky attackers. What matters the most is the board and how you manipulate them to your advantage, and having fun while playing this game.