What Are The Best Strategies for getting weaker tourney servers?

No strategy, just set your squad.

The only way to gane it would be to poll every single player in the world, sort them by difficulty, hope everyone was 1) telling the truth about when they'd set their defense and 2) doesn't have something come up last minute to change their time.

THEN, assuming the truth and no accidents, break them down into blocks of 5000 and enter the one with the lowest difficulty.

In other words: don't overthink it. Just so it.