Autofill matchmaking ~team 1 autofilled vs. no autofill?

When autofill happens in high elo ranked does the system auto fill an equal number of players on each team? And if not, why not. This a matter of fairness. Even if two auto fills on different teams likely are not equal, it has to be better than auto fill striking just a single team.

Cause it's not specified anyway at all so I assume autofill & Riot overlook "balancing" autofill between opposing teams.