Mafia 101. Disputed Island

The condition is clear, but have you considered alternatives? The first thing that comes to mind is: Number of townspeople + Serial Killer > Number of mafia members in one team * 2
To separate one mafia from another, because otherwise one might get lucky and recruit a lot, while the others are left out.
Or limit the number of attempts to recruit by one mafia to some number (3, for example). This option separates from everything it can, except for thoughtful gameplay.

The number of attempts should definitely not be limited. What if the mafia members keep targeting each other or the Serial Killer several times and end up alone, having exhausted the limit?

The proposed option is interesting, but it is still not an equivalent replacement.
Here is an example:

At the recruitment stage, there are 8 townspeople left against 2 mafia teams of 3 people each.
The first mafia recruits successfully. The result is 7-4-3. According to my scheme, the second mafia can no longer recruit, while according to yours, it will also recruit successfully, and the result will be 6-4-4.
However, you are right, it is worth considering other options