I don’t see the problem with Pryde saying Palpatine & co. “conjured legions of Star Destroyers”, I don’t think he means that they literally materialized the ships out of thin air. It’s just a riposte to that other officer calling them “conjurers”, he’s simply stating they have brought forth a large & previously unknown fleet, as if being “conjured”.

In any rate I don’t think Pryde would be privy to the inner machinations of the Sith Eternal and their ‘fleet conjuring rituals’, so I don’t see how this line could be read as him explaining the origin of the Sith Fleet.