Remember that God Magnus (RID Ultra Magnus) was never intended to be a version of Ultra Magnus, any more than RiD Grimlock is a version of Grimlock. Hasbro just reused these names to maintain trademark. I appreciate the God Magnus character too, but I don't see him as an Ultra Magnus.
The issue I have with Bayformers Prime isn't so much that he's different from G1, it's more to do with the inconsistencies and character contradictions. TF1 Optimus Prime only resorted to violence if he had to and took no pleasure from taking lives. Optimus Prime's plan was to stop Megatron, but failing that he would place the Cube into his own chest in order to merge it with his own Spark and destroy it. Ratchet reminded him that this would be suicide, but it was a risk he'd take to prevent the Cube from falling into Decepticon hands. Sam's idea was of course to take the Cube and shove it into Megatron's chest, killing him and destroying the AllSpark. And remember that when Sam had the Cube, Prime wanted Sam to give the Cube to him and push it into his chest, and when Sam instead shoved it into Megatron's chest Prime cried, "No, Sam!" Optimus Prime would sooner sacrifice himself than Megatron. Sam's decision is tactically more logical, but this showed us how TF1 Optimus Prime was more similar to the spirit of G1 Optimus Prime -- compassionate to a fault. Being more ruthless would make him a more effective commander but then he would no longer be Optimus Prime. This is the Optimus Prime that the first movie establishes.
Then in ROTF we see Homicidium Prime. The Autobots are leading NEST in hunting down the Decepticons, similar to how Cemetry Wind were hunting down all Transformers in Age of Extinction. When they found Scavenger and Sideways in Shanghai, they never offered them the chance of surrender. They looked like they were there to hunt them. Scavenger and Sideways immediately fled, and any NEST operatives that Scavenger killed was done so, really, in self defence. At the end of the scene we see a badly wounded and utterly helpless Scavenger. Optimus Prime then acts as judge, jury and executioner and executes Scavenger. They never attempted to capture and imprison these Decepticons - and we know from The Last Knight that the humans are capable of building and maintaining prisons for Cybertronians. Optimus Prime chose to kill Scavenger. And he even said, "Any last words?" before blasting Scavenger's head off -- this is at odds with what we saw in TF1 when Optimus Prime expressed regret over Megatron's fallen body, saying, "You left me no choice, brother."
Optimus Prime was already a veteran of the Cybertronian wars for millions of years, but he wasn't jaded. I find it incredulous to believe that after only 2 years he had a total personality flip just from hunting down Decepticon refugees. Really? Then there was the way that he seemed to relish killing The Fallen ("Give me your face!") -- again, totally at odds with his previous characterisation. And Revenge of the Fallen is a difficult film to defend considering that even Michael Bay has admitted it was rubbish.
DOTM Optimus Prime wasn't a whole lot better, again, the way that he just executed a defeated and helpless Sentinel Prime was in the same spirit was the way he dispatched Scavenger. Another execution of a P.O.W. Even if he felt that Sentinel deserved capital punishment, surely a sense of justice would dictate that Sentinel Prime be made to stand trial first. An international court could help decide Sentinel's fate and also help the humans to understand who was responsible rather than, ya know, allow Cemetery Wind to rise up and have all the Autobots be hunted down. Cos that sucks.
Okay, Optimus Prime becomes jaded in AOE and this actually makes sense considering how the humans that he fought to defend have turned against him and have hunted down and murdered his fellow Autobots. Optimus Prime's journey of rediscovering lost hope is a pretty decent one - the only character arc we see in any of the films. But AOE explains why Optimus Prime is so jaded. He doesn't suddenly decide to abandon the humans for no apparent reason. And even when he decides to care again, the movie does explain why. ROTF and DOTM provides no such explanation. He's just a bloodthirsty murder-bot now because reasons.
Killing all the Decepticons in Chicago or even the Vehicons in Hong Kong was different. Those were active combatants, not defeated POWs. He was fighting to liberate those cities from enemy occupation. When Sentinel Prime was defeated, the threat to Chicago had already passed. There was no longer any need to keep fighting him, let alone killing him. It's a war crime. The execution of Sentinel Prime reminds me of the scene in Saving Private Ryan - at the end of the Omaha Beach Battle - when American forces committing atrocities against defeated Nazi combatants (which is historically accurate). One scene shows American soldiers shooting into trenches to execute everyone inside. But there's this incredibly powerful scene where we see two soldiers in Nazi uniforms approaching two American soldiers with hands in the air surrendering. The Americans don't care about what the soldiers are saying and shooting them in cold blood, with one of them joking that they must have been saying, "Look, I washed for supper" and then laughing. These soldiers aren't even speaking German, they're speaking Czech! They're actually saying something like, "Please don't shoot us, we are Czech! We didn't kill anyone! We are Czech!" (feel free to correct me if my translation is incorrect) Germany had conquered Czechoslovakia in 1939 and many Czech POWs were forcibly conscripted from concentration camps into the Ost Battalion made up of combatants from Eastern European countries and the Soviet Union. And even the Germans in the trenches who had enlisted and chosen to fight for the Nazis were still shot in cold blood. This was deliberately done by Spielberg in order to show the audience that both sides committed atrocities in WWII - which is historically accurate. The difference is that Saving Private Ryan doesn't establish the soldiers committing these atrocities as being morally above that. Tom Hanks' character would be, and thus we don't see him partaking in this needless bloodshed. If Hanks' character had joined in, then it would be at odds with the way that the character was otherwise portrayed in the rest of the film. It would be as if he were two entirely separate characters blended into one... ya know, like M.J. Watson was in the first Raimi Spider-Man film.
I do agree that Movieverse Wheelie was an improvement.