Well, not sure about scenario 1. Vegeta told Nappa (who is much stronger than Radditz) to dodge Krillin's destructo disc because it would cut him in two. And that was a Nappa that wanted to tank it; tensed up muscles, Ki up. while in this scenario Radditz is supposed to not defend or even tense up his muscles.
I doubt that Radditz neck can tank an all out slash point blank. Like with max Haki, strongest swing, right into the throat.
But of course Radditz stomps the verse in scenario 2.