Yeah, MTU27 is an edge case. On the one hand, it doesn't include the Defenders at all and is really a Spider-Man/Hulk team-up. On the other hand, it's written by Len Wein, who writes the aforementioned Defenders issues that segue in-and-out of it. I believe it was skipped in Essential Defenders, despite MTU33-35 being included, so there's a precedent for excluding it. Personally, it's not a very memorable issue to me, so I'm kind of indifferent as to whether it gets included in a Defenders, Hulk or MTU Masterworks.