I think what it will stop is the rating inflation of the leach bots (the ones that play only a few rented cards with the starter decks). By playing many thousands of matches against each other, this is how the level 1 accts can get to gold (and in some cases Diamond) each season. Since these accounts are not likely to pay the fee, they will not be able to do this on the same scale.

This wont make the bots go away, but will severely limit their earnings or make them pay a big chunk of those earnings (via the DEC fee) to the game to be burned.

Of course some bot makers will continue to give up with each change too, so while it isn't banning the bots, its certainly reduces the incentives for their makers to spend time and energy