I certainly agree that there is room to do it either way and valid upside and downside to both. The thing that I dislike the most about what the 49ers are doing is they are betting on a big contract for a mediocre QB much like the Saints did with Carr. The difference is that the Saints kept the base of the roster and then tried to build around Carr, which isn't working so far but it has a better shot than what the 49ers are doing IMO. It just seems it is going to be more difficult to do for the 49ers when they have to build from the bottom with the same issues with paying big money for a mediocre QB.
As far as the Saints with Johnson and Young, I'm not a huge fan of bringing back Johnson, but only really because I think it's a year too long and a million or so AAV too high for Johnson. Although, if you look at the contract, it looks like it's really a 2 years deal with an out for the Saints before the third year.
As far as Young, I think that's the price they had to pay for missing on Davenport, Turner, and Foskey. Void years or not, they had not choice but to sign a relatively expensive DE in free agency and the void years, age, and upside made Young a better option than others. The deal is a year too long and maybe a little too high on AAV, but that's the price they had to pay for bad drafting at the Edge position.
Which brings me to what I think is the bottom line here. You can choose either option but both fail or succeed based on how well you draft.