I diagree. I think she basically becomes a modern day Pope in that while there is disapproval by the common populace if a leader opposed her, I don't see even Orlesians rising up in rebellion if it comes down to what the empress/emperor says versus what Leliana wants. Much less than places like the Free Marches and Ferelden.
A modern Pope is hardly negligible. Forbes rates him the 4th most powerful individual in the world, behind only the obvious rulers of the US, Russia and China, which might be going a bit far, but he's easily top 50, I'd say top 20.
Would Orlesians rise against his lord on Leliana's word alone? Probably not. Not even the Papacy at the height of it's power could make or unmake rulers at a word. But would her support be a major boost to anyone rebelling or seeking to raise a rebellion? Absolutely. Particularly if people felt Leliana's moral case was strong
Would you say that Leliana would STILL be against blood magic as Divine?
I never got the impression Leliana was ever particularly against blood magic. I mean, she'd be against the actually evil forms of it. But I mean, Leliana in Origins apparently thinks you should leave that Templar with the Desire Demon, and she is sympathetic to both a blood mage in the tower and to Jowan. And DAI Leliana is apparently cool with Morrigan's dark ritual.
Divine Victoria would probably find it politically expedient to continue to support full restrictions on blood magic though, simply because Mages practicing blood magic would be really bad PR.
What exactly do the mages have to fear if they decide to start practising blood magic again? It's not like she has any actual physical power to threaten them with
1. A good number of Mages would likely be strongly inclined to follow Leliana. She is after all not only the head of their faith, but was also personally crucial to their liberation. I mean, there was a "loyalist" faction even when the Chantry was a hell of a lot less friendly to the mages.
2. She could order the reforming of the Templar order. Let's not forget that a
dead Divine's support underpinned the creation of the Inquisition.
3. She could tell the Inquisition/the Seekers/National Governments to act against the Mages. Of course many of them are likely to do this anyway, but the Divine's condemnation of the mages would likely result in a stronger, more unified response and cut off any potential allies.
The mages need the acceptance of a world that hates and fears them. Divine Leliana is one of the few people with half a chance of delivering it to them. Pissing her off would be extremely foolish.