You dont have to pay anything every 75 days if you dont want too. The Matilda alone is practically the cost of the Battle Pass if you buy the pass. Let alone the fact that even if you did buy all the stages required to get all 4, you are getting 4 vehicles for what would be not even the cost of the T-10A.
Thats not also taking into account all of the other boosters, unique rewards and everything else included that are worth far more than what it actually is to purchase the pass or the stages required.
This also sidesteps the main point, that everyone can get a ton of things for free without anything. On top of all the usual bonuses of Warbond shops and on top of all the regular seasonal events.