Jebus Cross

It's not always possible to find judges, so you just need to limit the strength of the monsters.

What are the downsides?

The downsides are that it's a hassle for the judge when drawing lots :). Plus, the tournament result depends on them, and some players might get easier opponents (not significantly, but still). Therefore, it makes sense to run the Swiss system like a group stage, and the top 4 advance to the semi-finals.

The "tail" is eliminated both in a group tournament and in a Swiss system, which is normal, and it doesn't significantly affect the result of the "head."