that boss is a problem even to better off players. S-51 is really good her splash is much larger than rest of the 5*. Reason why skill does 1 dmg against maus is because maus has Aegis skill which reduces all damage to 1 but its a one time use and actually takes a while for initial use. Jagdpanther is probably the best 5* TD after seren and at a 4 cost as well.
Claudia you dont want same with the maus. 7 Cost is astronomical and is only used as an open with cheaper tanks and in addition the skill takes a while to charge up for a single use. Its still viable but only if you have mediums to follow up such as Meiling, Leo and t-44 for their high dps.