The option was always there for the users: run own dojo, which they always repeatedly and most users did.

Sending xpubs to dojo was not a whirlpool requirement (sparrow iust uses electrum servers). It was purely a UX decision to make the experience on mobile bearable.

They justified in an interview that for the postmix account (which can have hundreds of transactions), using block filters requires gigabytes of network traffic. For mobile that is simply unacceptable.