It's slightly better than Orsino as it at least had an attempt at justification with the plot device idol but mind control/corruption is almost always lame and this time wasn't an exception. It's a convenient shortcut for weak writers.
Like with Orsino, it undercuts the already very weak payoff for choices in DA II and is also poor writing in a game that was ostensibly trying to be more human and political in a move away from a completely black and white conflict like with the Darkspawn.
I agree. The worst part of any mind-control gambit is that it both removes personal responsibility for any crime from the part of the perpetrator, while simultaneously deligitimizing any points they might try to make in the view of the player. For the first, it can be blamed on artificial insanity. For the second- well, if you already don't like the point, clearly it's insanity.
More to the point, artificial insanity is a crutch that isn't even needed. Rather than being a lunatic with a real problem, she could be a hardliner with a real conspiracy on her hands. Likewise, I thought the Orisino reveal of supporting Quintin was a bit ham-fisted (and selectively revealed): it came far too late to have any significant impact. It helped turn both characters into caricatures, when they could have been simply sane but irreconcilable.
In that hypothetical alternative world...
Rather than treat the Circle Mages as the innocents while evil foreign mages prowled the streets, I think it would have worked better had there been a real and acknowledged conspiracy within the Circle itself that was seeking to get mages out and instigate a political revolt against Meredith. Rather than just Tevinter agitators or apostates in the streets, a real actual coven or conspiracy acting within the Circle working for the same revolt. Meredith's emergency powers become the basis for the cabal to try and instigate a political revolt against the Templars which justifies Meredith refusing to give up power when a maleficar cabal (including possible blood mages) is playing the disatisfied nobles.
Meredith without the sword excuse and degradation would be pretty fine in its own, especially if she treated the problem as a military one requiring an uncompromising stance. Rather than pointless lockdowns and illegal tranquility and executions, she could instead be effectively declaring a state of emergency within the Circle and city as violence is spreading. She can still be held responsible for the conflict (her initial holding of power being the initial political dispute, her hardline attitude inflaming tensions, her crackdowns pushing more mages to support the cabal) without being insane.
Orisino... his flaw should shift from the Quintin issue to a more openly addressed issue of being a poor and unfit leader for the mages. He opposes Meredith in the name of all mages, but his sin would be that he really doesn't try to keep the mages in line or stop the cabal. He's an enabler, rather than being complicit, but his obstruction and defense of even clearly guilty mages is creating more and more problems as the defenses and checks of the mage-templar divide are becoming naked legalistic shields for the cabal, and so Meredith is gradually tearing them down. Orisino should be the sort of First Enchanter who is basically a mob lawyer, using the law to prevent justice and the apprehension of real criminals.
If you wanted to have a pre-climax/lead-up to the Anders explosion of The Last Straw, you could even have last story mission (and false climax of the arc) be a mission to root out the cabal (in hopes of resolving the tensions) that finds evidence of a blood magic mind control plot against Meredith. Meredith's increasingly uncompromising extremity is a consequence of mind control attempts intended to either mitigate Meredith's uncompromising nature, or to increase her hostiliy towards mages to spur tensions. The cabal is coy about which it was, but letters indicate they have been counting on Orisino's interference to conduct their operations.
Thus comes a moral choice, and seeming lead-in to a big decision. Do you give the evidence to Orisino or Meredith? Orisino would hide the part about the cabal relying on him, but would use the evidence to undermine Meredith by insinuating that her paranoia and power grabs were a result of blood magic tampering, and that she is too compromised to remain Knight Commander. Meredith would cast the blood magic attempt as a failed attempt to deter her from her course, and use the letters to try and remove Orisino from his position as First Enchanter and enact Templar-only emergency rule of the Circle. Whichever side you choose cues the fight that starts the scene, and the confrontation at the steps of the Chantry as neither will let the other reveal their information to Elthina.
Cue Anders, the wildcard who blows up the last moral authority figure, and the confrontation. Meredith is convinced the Circle is corrupt beyond salvage (a position the player has more reason to agree with) and calls for annullment. Orisino recognizes that the Circle is corrupt, but doesn't intend to let Meredith punish them all regardless.
Same delimma, different angle of approach. Meredith comes off as a bit more understandable, since she's less insane, but Orisino is still reasonable if less sympathetic as a not-so-innocent victim.