So here's the gist.
Duke starts crippled. Samus is all but worthless without her armor since all her weapons are built into it.
It's going to take a little while to find the other team in Lemu, but they won't be doing any sort of buffing before then with all the healing that needs to be done. Jake probably wastes most of of his mp just healing Duke (and trying and failing to do it for a while). Sephiroth and Ryu's clones and Luca's wolf will be the deal breakers here-- Ryu can use his clones to scout ahead and generally confuse/overwhelm the enemy and Seph if killed will come back with another clone and the knowledge of what killed him (and the element of surprise). Luca's wolf can also scout and absorb firepower to little effect since it'll respawn.
Basically there's just not enough damage output on the other team to kill all of Seph's team before they go down. Jake, Hibana, Duke, and Samus are all squishy enough that Ryu can chop their head off with one flying swallow. Chief is durable but he can only do so much.
Even if you buy buffs getting put out, Seymour Omnis has multi-dispel which will remove all buffs from the enemy team.
Worst comes to worst Lemu breaks apart from the combat and Seymour Omnis is the only one who can deal with water pressure and being thousands of feet under water and he wins by default.
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No problem!
This is a cute and pop genocide of love!