Were Avon and the others desperate in Blake? I'm not sure. It's not like they had nothing left. They still had each other, Avon's brains and skill, the antidote, ORAC and the Scorpio with the teleport and the stardrive. Which is far more than they had at the beginning of the season.
I think they certainly had more than Blake. Let's see what Blake had.
A base and the beginnings of an army.
Hmm, this is a base where Blake can't even use his real name, right? What kind of base is this?
The beginnings of an army, well he must have just started because it takes almost no time for the Federation to enter the base and get clear to the command centre and by then there is no armed opposition other than Avon's people. So Blake's army consisted of what? Blake, Arlen, Deva, a couple of unarmed technicians and...two janitors?
He had his own computer expert. Uh, this is Deva, right? Who is so successful in breaking into Federation computers that he can't tell Arlen was a Federation officer? It was probably because of his failed efforts that alerted the Federation to Blake's presence on GP in the first place because it's not like Blake was advertising his presence.
Plus Blake was trying to buy weapons from people who tried to kill him. Don't think he got any weapons and we do not see anyone on the base armed other than Blake. And Arlen but I think that was her own weapon.
Not to mention, Blake by now seems completely insane. And he looks like he's had a really rough time of it since he left Avon. Blake is now paranoid to the extreme, can no longer even tell who he can trust anymore, and physically he looks like he's just gone ten rounds and lost every one. His own right hand man thinks what Blake is doing is stupid and the way Deva talks to Blake sounds like if he hadn't made the promise to stay with Blake, he wouldn't choose to be with Blake at all. Sounds like he's his lost respect for Blake and has been trying to work around him.
Avon had far more than Blake at this point, plus he was at least sane and he does not look like he's been through a cement mixer several times.
Blake is trying to eke out an army among a group of criminals and a planet that is begging to be let back into the Federation. He's just been thoroughly duped by a Federation spy, not even their top one, and he's once again about to get his own people slaughtered in a Federation trap.
Blake was the desperate one in the final episode, not Avon. Avon almost saved his sorry ass once again except that this time Blake's arrogance and stupidity was his downfall.
The warlord plan fell through because of Servalan. I think Avon just went to plan B. Not because he was in any way desperate but because it was his second best option.
And I don't think Avon ever intended to let Blake lead again. And I don't think he would have allowed Blake to if Blake survived. Avon is a different man now, not easily bullied. It's because Blake didn't understand this that Avon killed him at the end.
Blake can no longer get away with not answering Avon's questions and thinking he can order Avon around just because he was Blake. Avon is no longer susceptible to Blake. He is just as strong now and can not be pushed around any longer. I think Avon planned to use Blake in the same way Le Grand and his cronies did. Use Blake as an empty figure head. Feed his enormous ego with platitudes but the real power would belong to Avon. Just like Le Grand and his bunch tried to do. Perhaps that's where Avon got the idea from.
I think Avon was telling the truth that he knew where Blake was all along and planned to leave him on GP if the plan had worked. He probably only had ORAC look for Blake just to make sure he would never even accidentally run into Blake and to make sure he would never be fooled by Servalan again. I think that was why Avon went to the warlords instead of the rebels (which is far more logical) because he wanted to avoid running into Blake. Because he was very sincere in Star One when he wanted to rid himself of Blake and talked about Blake like he was a disease he wanted to be free of. And I firmly believe what Blake finally realized, that Avon not only hated Blake, he really hated him. Though, Avon did have a little love left for him, enough to not want to see him dead.