They are fascinating. The most obvious one to me is the sending of the twelve. There is absolutely no reason verse 30 should not come after verse 14 with 15-29 following as its own material.
Pillar? It is a solid commentary. I disagree with him slightly on dating though. I think Mark comes just after the destruction of the temple (ca. 70-75) not before (64-70C.E.). Oddly enough, it may have even come from someone immersed in Petrine teaching. I have little reason to doubt the connection anymore( though this doesn’t mean what some think) and it comes early from the Elder who Papias depended upon.
The literary features of Mark are hard to unravel. I waffle back and forth all over the place but the existence of sandwiches is not one of them. Its a fascinating subject!
Vinnie