For me I think it's fine as it is.

How you place and set-up your team do count towards activating mysteries.

It can be strategies on player to have a few ninjas at the backline using Mysteries i.e. Gakido, Jinpachi etc to bait out round 1 interruptions.

Unless your enemy has only Han activates Mysteries, then your Itachi will chaos him.

Your interruption would likely auto-aim to least HP ninja, which is at the back where that one has worst equipped items. And that it goes the same "mechanism" as other auto-battle where your pos 1 at Round 2 would likely to aim least HP in the field.

Round 1 all ninjas have full HP.

Your enemy, Pos 2 (Team A) and Pos 4 (Team B) are using Mysteries at the same time. Pos 4 (Team B) is more likely to have less HP than Pos 2 at full HP and that's where your Itachi's chaos goes.

This is only a theory. It could be wrong. You need to check those position HP yourself.

If you're really confident that your Pos 2 is faster than enemy Pos 2 Han. Get Shaky. :P That's another way to counter removing shield/buff in Ranked Battle.