However, spend $100 on WGT and suddenly you shoot 52s instead of 67s.
This is arrant nonsense.
Spending $1 million on WGT will not make you shoot 52s suddenly or otherwise. The combination of practice, practice, practice and upgrading your clubs just might though, eventually.
The game is fixed. Just accept that.
You have made a perfectly valid choice to stick with the starter equipment and not spend any money on upgrading, just like the OP (two years ago). This game can be perfectly fun to play that way and I sincerely wish you many contented hours of happy hitting.
But if you have some expectation of being able to be serious contender in WGT tournaments and possibly even winning a bundle of credits that way then you will need to upgrade. Any belief otherwise is not about the game being "fixed", it's about you deluding yourself. Just accept that.