User blog comment:Observer Supreme/How would Kizaru and Aokiji operate if either of them were Fleet Admiral?/@comment-24850639-20170718191705/@comment-25400375-20170718193502

Talk about a long, yet good, read.

I think the Yonko are largely left alone because their crews can be considered to have military might on their own. The Marines really took a huge gambit in fighting Whitebeard which probably would've led to a Yonko battle, if Blackbeard didn't take the reins, crooked scoundrel though he may be.

Regardless, your assessments of Kuzan and Borsalino seem right on enough.