The standard WAR positional adjustment for COF and 2B is a 10 run differential. There are additional scarcity adjustments. If he's a very good CF or and/or an elite COF then there's less of an issue. I'm not sure that's the case. The guy's power and walk rate are also red flags for me in the OF. You can typically fin find better offensive profiles, otherwuse we're leveraging heavily on his defense. Of course he has to be able to play second base, but yeah, I do think he may be more viablel there. I agree a lot depends on how good a CF he could be.
Right, the adjustment between 2B and LF is 10 runs, but there is no adjustment between CF and 2B, both are +2.5 runs per year. And there are no other scarcity adjustments, IMO, the positional adjustments incorporate all of that. They are meant to be inclusive of longer periods of time, so I suppose you could scale them differently year-by-year if you like based on the rise and fall of offense at a particular position. I've always considered the adjustments to be more of a bonus for players who are capable of playing a higher rung on the defensive ladder. No bonus points if you can't get on the field (DH), +5 runs if you can handle 1B, +15 if you can handle a corner OF spot, +20 if you can handle 2B/3B/CF, and +30 if you can catch.
Versatility is always a good thing, especially for a guy with a questionable bat who may be better suited to a utility role. But I'm much more interested in how McKenna hits next year than how he fields.