The Grey Nayr wrote...
1. The Citadel fleet got decimated by the Geth when they were actually prepared for the assault. Even the Councilors believed they were more than ready when they refused to let Shepard go to Ilos. But they were wrong and if you don't let the fifth fleet save the council, the Standing fleets gets all but wiped out. If they had been hit by a surprise attack, it would be a lot worse(it's common logic that a surprise attack works better than a direct offensive because it catches your enemy off guard and unprepared.)
2. "What business does Saren have there"? Are you serious? I answered that in the very comment you're asking about. Saren would lie and say he is there to protect the council, just like Ashley/Kaidan did in ME3. Spectres are top agents who answer only to the council, so it's not unreasonable that they play secret service when need be. And C-Sec can't tell them what to do or where they can't go, only the council can do that, and they loved Saren so much before Shepard proved him a snake that they'd welcome him as their bodyguard.
As for Saren not standing a chance against C-Sec, none of them would expect someone who is an honored and trusted agent to attack them from behind. Also Saren has more to use than a gun. He's got Reaper tech implants that enhance his performance greatly, on top of giving him biotic abilities on par with the Asari(Paul Grayson had the same implants and abilities and was able to take out an entire ship full of armed Turian soldiers by catching them off guard. Proof of concept)
3. Are you serious? It's never not practical to indoctrinate someone. The purpose of indoctrination is to create double agents for the Reapers. And close proximity to any Reaper tech(not just sovereign) that isn't properly shielded can cause it(people in ME1's side missions got indoctrinated just by digging up Dragon's Teeth. They had no contact with Sovereign.). It's subtle and practically unnoticable. And Saren's body is loaded with Reaper tech. He could probably indoctrinate a councilor just by handing in a report in person(rapid indoctrination).
You have to make assumptions that contradict plot points and information in universe to make this one man assault work.
1. The Fleet isn't the most important point there. It is closing the Citadel arms. If they are closed before Sovereign makes it inside he is stuck and cannot take control of the Citadel to determine what the sabotage was and how to reverse it. It doesn't even matter if Sovereign himself is a match for the patrol by himself, if he is stuck outside the arms all he did is present himself as a threat to the Citadel. It is described as impenetrable with the arms shut, he wouldn't get in.
The main issue is you seem to think there wasn't any security on or around the Citadel prior to them taking Saren seriously, which was is false. Demonstrated by discussion about Control, standing fleet, C-sec. To make the assumption that security was so lax that one agent could take it, you then are stating that Saren was an idiot for not realizing it, Sovereign was an idiot for not realizing it after learning about it through Saren, the council and C-Sec are idiots for not protecting the only defense the Citadel has, etc. So if you want to claim that everyone in universe is an idiot and you were smart to realize this plan would work, despite having incomplete information, go ahead.
2. I'm very serious. The player never goes to Citadel Control (where they operate the arms, not the Council Chambers) in any of the games. You do not have any proof that Saren has access. Even if he can get in with some absurd reason (which makes no sense since the Council isn't in Control), he still has to manage to kill all the security there himself, and hold it until Sovereign gets into the station.
What are you on about with Saren vs C-Sec? After he kills everyone in the control room it won't matter if he was respected, he is clearly a thread and a criminal. He has to hold Control from that point until Sovereign arrives through the Widow relay until he makes it to the Citadel. Sovereign cannot arrive in system before Saren takes Control or the arms will start to close before Saren can intervene.
Saren has no Reaper implants until after Virmire.
3. Not believable. Saren doesn't have implants until after he has doubts from his conversation with Shepard on Virmire. So that is debunked. Sovereign is the main source of indoctrination for Saren, Benezia and her staff. Yes, Dragon's Teeth did indoctrinate some people on side missions, but it is not believable that they could simply be brought into the Citadel and used to indoctrinate anyone important, least of all the Councilors. "Oh let me just leave this random artifact here, don't pay attention to it." Indoctrination isn't instant. And if staff on the Citadel start to behave oddly all that will do is arouse suspicion and increase the risk of discovery of the Reapers. It is one thing for a random mining team to find an artifact on an uncharted world. It is another to simply bring them to the Citadel and leave them in the open.