Since stacking pos 1 is a thing in this game, shark bomb teams are simply great. And if you think it's broken now, just wait for the release of skillbreaks and ninjas that can remove immunity with chase... like SB Hanzo.

But... water main is reknowed in CN to be the only main who can't provide immunity with his skillset, which is a great malus in modes where you can't run sharkbomb (arena, matsuri).

Fire main won't change much. His immunity mystery is just too good to run something else. Seal might be fun to run against a few teams (fire main pos 1 and edo hiruzen pos 2 is awesome if you outspeed the enemy pos 1 hiruzen), but is nowhere as strong as a full team cleanse + immunity.