The rank of Admiral simply reflects his seniority in the Navy since he obtained the rank of Post-Captain.

You clarify better in the rest of the paragraph, but bear in mind that there would have been hundreds (thousands?) of officers of similar or longer service, but of inferior rank, who would also have been considered successful.

Easy going, Laid-back.

Let's keep in mind he's now discharged. In command of a fleet, and earlier of a ship, easy-going and laid back are not generally (if ever) useful traits.

Unpretentious

Definitely an advantage in a wartime military; definitely a disadvantage in a peacetime military. Or so I've read.

I like your comments regarding his marriage, but it seems to me that in many cases you see clearly his superficially relaxed and oblivious persona, and less clearly his deeper sharp, very aware perception.

For example, "there seems no harm in" Sir Walter I see as wry rather than tolerant.