You really are hung up on this conspiracy theory …. But that’s not the case.
There’s plenty of reasons why a Supercharger won’t deliver maximum kW; or in this case, half of maximum kW. Everything from current draw to charging handle temperature can affect it. Lots of factors, exactly none of which involve the payment method (or, lack thereof.)
I’ve got a 2020 X with free Supercharging as well, and routinely see everything from 250kW down to 12kW, and lots in between.
I also have a Model 3 which does NOT have free Supercharging (although I do have referral miles), and get the same behavior.
All normal.
I guess Tesla stopped updating the older MX. That's first time I've seen the supercharger graphic!