I should have been more clear, I wasn't saying WG won't ban whales or any other paying customer just because they paid the SerB tax.
Look at this from the other direction, what would happen if WG did ban all these shitters? Yes, gameplay experience for a lot of people MIGHT improve, but at the same time WG is also cutting off one of their revenue streams. A happy shitter is a paying shitter, and having paying shitters is a lot more important in the business sense than appeasing a smaller population of non-shitters (who are also paying customers anyway). It is very possible that non-shitters may be willing to invest more into the game if there are less shitters running around, but why would WG take that risk when they have perfectly healthy money streams right now?
Also taking into account of the power of publicity and social media, if WG indeed goes forward with banning shitters but cannot handle the backlash, the negative publicity will potentially drive existing and future paying customers away, as well as putting huge amounts of pressure on the company when their efforts could be better spent on drumming up new ways to milk people dry. Shitters are loud and numerous, when they throw enough shit at the wall some will eventually stick and people will come to look at what all the fuss is about. Recall how blown up the Sir Foch incident became when WG EU took the proverbial slap to the face and got humiliated, now think how easy it will be to spin the story of WG banning shitters, "WG issue arbitrary mass bans for no broken rules". This is bad publicity that any game company will want to avoid.
This isn't to say as long as you're a paying customer WG will be more lenient to you. Rather, WG wants to keep their current and future paying customers happy for milking. Shitters owning a bunch of prem tanks is a testament to how true the mantra of "happy shitters are paying shitters" is, WG understands that.