What makes you think of Jean-Luc Picard was a powerful Admiral? He obviously reveled in his own notoriety; and certainly thought more of himself than the admiralty did. I mean in Picard season 1 he's shown as utterly shocked when the admiralty calls him on his threat to retire, and basically says... "Okay that's fine. We'll accept your resignation.."I find it implausible that one of the most powerful, important admirals in all of Starfleet wouldn't at some point learn that one of his former closest officers, whom he spent years mentoring, had rejoined Starfleet. If nothing else, that seems like the sort of thing that would inspire someone to tell him out of personal loyalty.
^^^
Jean-Luc Picard honestly thought that such a threat would be a trump card. He could never imagine the admiralty allowing him to leave...until they did so, and that really burst his overinflated ego.
I mean if he really did care about helping the romulans relocate; after he resigned, you'd think he'd still use whatever pull he had to do whatever he could as a civilian. But no as soon as that happened he retreated to his Vineyard and just started making and selling his wine.
He was nothing but a show Pony for Starfleet recruitment over the years. The real Starfleet Admirals were working on keeping the Federation Alliance intact.