A resolution without dissent is only required when you are doing something drastic, changing unit entitlements, passing common property to a lot owner, etc and it should say in the WA Act what these situations are.
It’s a pretty safe bet that opening a bank account is NOT one of them, as it is such a trivial issue. I would say the SM could change the bank account without any vote whatsoever (and the SM should know this anyway).
The only situation where you MIGHT have a problem is if they registered a special bylaw specifying which bank to use. But even then a developer who controls all the lots initially has a duty of care to not do anything to prejudice subsequent owners, and I would say this fits the bill exactly.
I know nothing at all about WA strata this is just general info which applies to some state (NSW & QLD) but I suspect it would apply universally in Oz.