The difference is Lucius wasn't really a leader, he was a saboteur and traitor with motivations and goals completely different to Fiona's. Trying to compare them falls flat because they have little in common.
Furthermore a big difference between the templars and the mages is that it took active sabotage to make the former fall while the latter were destroyed by their own complacency and negligence.
Case and point the templars not knowing about the Envy demon. That happened because the senior templars who could recognise it were disposed of before hand, a smart move. Fiona signing over the mages because of a non-existant templar army? That happened because she wouldn't even do basic follow up on information she received, incompetence.
So, Fiona gets called a bad leader because she made mistakes while trying to help her side... bu Lucius was sabotaging his own side and wanted them all to die, yet he gets a free pass on being called a bad leader?
(And I've been accused of being biased... wow?)
Wait, confused, which side was complacent and negligent? Those terms equally describe what the Templars suffered because they accidentally allowed a demon to take over, while the upper ranks where either bumped off or quickly corrupted. You'd think that in a war with Mages who for all they know, might summon demons to fight them, they might be a little bit more on their guard?
Dras, you keep referring to a non-existant army as proof of Fiona's negligence, ignoring the numerous times when it's pointed out to you that the Templars were in the Hinterlands before they withdrew to Val Royeaux, leaving only the deserters behind? Doesn't this suggest that they had some kind of presence in the area to make the Mages feel threatened, thus giving cause for her to fear an imminent attack?