So, let's try this again. To make whatever level of income, some prices are chosen. Those prices can be lower to get to the same level of income if we don't have the sharing. If we do have the sharing, the prices have to be higher to get the same level of income.
It seems like this reasoning assumes that the number of "real buyers" is fixed, and then the issue is to get as many of the others (who would just use other people's cards if it's possible) to also buy. But the number of "real buyers" isn't fixed. They look at what it costs and what they get. Getting cards that you can use in matches against your friends and cards you can use in matches against lots of unknown people (so you can get quick and good matchups) is worth a lot more than cards you can only use against other customers.
My view is:
Paying customers should get good matchups (matching their criteria whatever they are) quickly, and then of course they should get to use all their cards in those matchups.
Sometimes it will be possible to match them with other paying customers. Then do. Sometimes it won't. Then even the players who never will pay a cent is a
resource. They are like prop players
you don't have to pay! When they aren't needed those can be matched against each other and play all Base Set games.
The main reason is to make what is good for paying customers. If there were a freeloader being one of the top players that player would probably often get to play with all cards anyway. That is not because we want to reward the player for being good, it is just because there probably are paying customers who would like to be matched against that player.