I posted this idea in another thread, but thought it might be worth bringing it up to you directly! Have you thought about the idea of dynamic trader pricing? That is, instead of having global limits or personal limits, make it so that the more you buy the same item, the more expensive it gets. This simulates the real world where a trader would see that a certain item is "in demand" and raises prices (like GPUs in the real world during pandemic). After not buying that specific item for a while, the prices would begin to fall back to their normal price again.
For streamers and rich players, it would let them keep buying the gear they want, but they have to invest a LOT of their rubles. For the average player, it lets them just buy what they want for the few raids they play. This will act like a big money sink for the hardcore players that dump a lot of time in.
If the streamers/hardcore players don't want to waste their rubles, they can purchase alternatives instead. This would force players to use more of the inventory of guns/ammo/armours and make the meta more diverse. When I was grinding Tarkov in my most hardcore season, I was logging in every few hours to buy gear or craft ammo on reset. The limits essentially didn't matter to me because I would log in every few hours, and have enough ammo and gear to run that night.
This simultaneously could help to fight the stale meta issue, the frustrations for new/casual players, as well as act as a ruble sink for late-game players.