Oh, indeed, Boromir has many good qualities, but I'm not sure he really has what it takes to be the head of a large nation engaged in a long war with a superior power. Not at that age, anyway.

I imagine Ecthelion being much the same, and I bet that contributes to the part of Denethor's love for Boromir that is unconditional.

This is very plausible, as I think is the idea that his sunniness reminds Denethor of the Finduilas he married.