Previously I would very patiently stealth through this section but the absurd amount of critters now makes this approach basically impossible without a lot of save scumming and luck since on top of the increased numbers Roderick has a penchant for attacking the critters on his own and him dying means automatically a reload since you cannot escape from the island without him. What is even more hilariously stupid and immersion breaking that in real time the PSI beetles tend to no use PSI at all and just rush to him in melee. It bums me that the Silent Isle is now basically a combat exclusive area.
For what it's worth, though I *sometimes* have to load once or twice (the Captain can get randomly engaged over his head, luck does somewhat factor in) it is very much possible to regularly one-shot (no save/loads) (with stealth builds) under level 10. Do you have interloper and optionally some cheap ninjatabis with +speed or other initial stealth gear (and maybe an Agility steak)? Are you using adrenaline in the "safety" area near the crystal room transition for a quick grab? Are you using combat-controlled stealth movement to your advantage (it freezes enemies in place if they don't see you yet)?
I have *never* used damage-dealing to complete Silent Isle on Dominating and I've completed several such runs now (and even more completing at least the Silent Isle...always go on the Azure bug side).
However, the way I approach Silent Isle (and the rest of my runs) is to semi-scientifically break down and analyze the geometry, movements, skills, and tactics needed. I agree with you that you can't just willy-nilly stealth the island like on lower difficulties, but I feel that that is kind of the point. Dominating *forces* you to fully optimize for what you want to do and go all-in on doing it and will still heavily punish you if you make execution mistakes. Unless I'm misremembering, this difficulty is specifically designed for people who already know the game from start to finish.
So it's in no way true that you *must* fight to complete Silent Isle or that you *must* have save/loading in order to use stealth there, but it definitely has potential for bad luck and very thin margins when stealthing.