On a vacuum, I agree with you and the energy of your post. Being inadequate at PF puts the Spurs in a lot of losing positions, which is perfect for the short-term tank. The issue to me, is how the Spurs approach Keldon (and the starting PF position as a whole) moving forward - do they recognize Keldon's inadequacy, and draft or trade for adequate talent to fill that hole, or will they double down on him as "PF of the future" and lock him up to a sizeable contract? It's his FA that worries me the most, not Lonnie's and not Devin's, tbh... It'll signal a decisive longer-term view from the FO rather than the immediate "just play him there since we have no other options" plan Pop is going with right now.
Of course, drafting a top-talent PF prospect could be an easy solve for this too. But I'm wary of assuming the Spurs will draft for height, after all these drafts, and especially Primo... I'm fine with BPA, even if it's a guard, but the above has to be taken into account in such a scenario, IMO.