If will force them to level 4 times to reach the same efficiency. This will slow the influx of new bots, which is the real problem. If blizz bans bots right now they are simply replaced within two weeks. In case you haven’t noticed, the amount of bots leveling has decreased lately, because banning reported bots didn’t work. They were being replaced faster than they were banned.
Likely this along with the authenticator incentive of 4 extra bag slots, is a push at sealing up the influx of new bots, so that banning will actually have an effect. The authenticator incentive will reduce the amount of player accounts that are hacked and turned into bot accounts.