It's incredibly slow; easily flanked; 13 CP and by the way costs the equivalent of well over 300 fuel.
I think it's fine as is. Given the aforementioned cons, nerfing it would make it go the way of the Elephant (i.e., the Dodo)
Problem is that is has extreme range, shoots like a Pak43, doesnt really get stunned once upgraded, and even when flanked, support is more than happy to clear things up. Its extremely hard to kill that thing against decent players, while this fortress shoots through buildings at extreme range 2 shotting most of your armor.