Except for the one year prep thing where they could just attack Doom and take his time machine. The Techno Lords all jump back in time before Legion and Franklin existed and kill their parents. From that timeline, the Bots spread out and incorporate their future tech the past tech and again take over Earth with the same strategy as above. In fact with Henshaw and Ultron's ability to warp tech and alloy, the can build an army in hours or at most days. They still have access to the Fortress of Solitudes tech, Batcave, Cerebro, Nimrod's future tech, and Brainiac's vast database of knowledge. The create a new timeline where the machines win. The old timeline becomes an alternate timeline.
The machines still take this. The machines are too smart not to do something like this.
I assume the year prep means they have a year to prepare, then they can actually attack the Earth, so they can't just kill all the heavy hitters in that year and attack an undefended Earth.
Either way, taking over Doom's armour would not be as easy as you're making it out to be. Admittedly from purely a tech point of view one of the high end technopaths could do it, except for the fact Doom has (iirc) a number of magical safeguards and protections worked into his armour.
And although the machine are smart, there are still a huge number of incredibly powerful beings on MU/DC Earth which they will not be able to counter easily.
High end reality warpers/Molecule Man/hundreds of gods etc.
Sure it could be argued Amazo instantly appears and adapts to their powers, but a number of them will be incredibly difficult to locate, especially if they realise they're being targeted.
I'm certain he would murder amazo if he confronted him in battle. However, I don't see amazo confronting franklin, I see him passively copying his powers. In all seriousness, iirc, all he has to do is look at him.
His armor has magical encantations that protect it for alloy manipulation? When did this happen? Henshaw and Phalanx Ultron can warp the metal on his armor to crush him.
Which all each eat we placed nukes teleported or planted thanks to Brainiac. Within the first few weeks, Batman's database, the Fortress of Solitude, and Cerebro are all used to locate these beings. Then for the rest of the year they'll develop a strategies to counter all of them, including neutralizing their powers.
Which gods reside on Earth? MM can have his powers stolen by Brainiac. They would need to just steal Doom's tech, not hard these guys.
Cerebro, Batcave, Doctor Doom's database, etc. They have a year to do this, it's a long time for Bots that can instantenous take over non-sentient machines.
And if they ran through databases of past history, they could reassemble Archenemy.