Of course. But you will have even less control over things if you remove yourself from the timeline entirely, and risk things far more if you take what used to be your targets biggest ally and remove them.
The shock stuff only applies to first moments after receiving the intel. Soon after he could easily realize it's better to help mc directly. Besides, the whole "make mc king" plot was something he hatched before sending the memories, so it wasn't an "in the moment" decision.
He doesn't have to deal with the nobles instantly. He could have easily let them start being belligerent, and then use that as an excuse. Or pretty much anything. The point is that he would have far more options and control if he remained king (including making mc king later on), or at least remained by mc's side after giving him the throne. Could have even left the nobles alone, or fabricated evidence (or used real evidence), or whatever.
And that is exactly a great point for not making up his plan to take effect instantly on return, without consulting anyone (if needed, could push the return further back to before the summoning, to have more time to consult ppl). He could have even asked mc himself, if he gave it some time. Or the dead general.
Why would he need to instantly purge them? He could delay it etc., or he could not do it at all, etc. But if you think the best option was to purge them instantly, then I would say the best option would probably be something like framing them (or use evidence you know of from being a time traveler, if you know any).
As for the 3 dukes, supposedly some of them would believe his story about his wife's power (maybe even prove it somehow, like using it again). Or he could simply let them know about the reality of their crimes already committed - the nobles were all ones who had done enough crimes to get executed either way (which was what mc found evidence of and why they rebelled), so would not be hard to justify mobilizing the dukes.
Hell, he could even use the exact same plan he did, even if he didn't force mc to be king. Or if he helped mc by not holing himself up and rejecting all audiences by his [new] lord. And worst comes to worst, abdicating after being denounced as a form of taking responsibility, handing over the throne to his daughter, is still an option.
Or pretty much any option would've been better than forcing a risky war on an unwilling, new, inexperienced and untrusted king. Mc luckily won each war somehow, but from the timeline king knew of, he had no idea about mc's prowess in war.
As for telling mc the future, it depends on how much he trusts mc's capabilities- if he thinks mc would do a better job as king blind than him with future knowledge, he would surely think mc would do an even better job with said knowledge.
Overall you seem to be making a whole lot of wild assumptions regarding how various things would work out, like I don't follow how king would know that the restoration would be doomed and ignored by mc, if mc knew there were a civil war coming soon.
He could have remained a 'normal' king, and still had mc handle things. Even full authority could be given without handing over throne and leaving him to drown.
George's plan was still not very good, as all it did was give the traitors a fighting chance in a war mc almost ended up losing if not for being much better at war than king expected.
King couldn't have known about any of the ppl souma gathered, would be a risky move to expect them. And souma had little need to grow as a person, particularly as king couldn't know whether he actually would or not. Actually being taught kingcraft akin to some sort of apprenticeship would likely have had him grow way faster. And far less risky.
