The Office of the White House Counsel to the President has not been mentioned in this discussion. This is not the president's personal lawyer. The Counsel reviews every document the president signs, all major speech, and all policy decisions. Just about everything a president does within his duties as president is reviewed by White House Counsel for violations of federal statues, oath of office, and ethical considerations. The bottom line is it would be very rare for a president to break any federal statue. Full immunity from civil or criminal prosecution is at it's best is unnecessary and at it's worst might encourage president's to violate the law since there would be no penalty.No false claims, just rephrasing your arguments to expose their weakness.
I already acknowledged that your point that you don't want the president (although this would logically apply to all civil officers) "second guessing themselves".
My response was already stated. One, they should be worried. Everyone should be worried about the legality of their actions. That's a feature, not a bug. Two, there's already a system in place to protect a president (or civil officer) from malicious prosecution. For one, the DoJ has a code of ethics to stand in the way. For two, the justice system protects people from malicious prosecutions. That's what the judge and jury is for. That's what proof beyond a reasonable doubt is.
The next part of my response you likewise ignored. Immunizing them from criminal prosecution would prevent them from being subject from malicious prosecution. It would also protect them from justified prosecution for actual crimes. As I said earlier, you can't immunize them from one and not the other.
So there's a cost here, that the president (and civil officers) would be emboldened to commit crimes knowing they're protected and the hurdle to criminal prosecution is extraordinarily high. The benefit (based on my argument above) is minimal since they are already protected by the justice system.
As for your discussion about what is in their official duties (and your annoyingly excessive use of the word ambit, give me a break), I also responded, which you ignored. It blurs the lines of what we ae talking about to the point that you're basically creating a situation where the entire doctrine is irrelevant.
The idea of the action being within their scope of their duties does not mean it's legal. The question I posed is whether you could prosecute Biden for making the DoJ go after Trump for personal gain. Is that within the scope of his duties? What about taking a bribe for an official act? Is that within the scope of their duties? It's hard to know what you exactly mean here, because one would assume that any action within the scope of their duties would be "legal" because their duties are legal.