How? ODST is a spin-off of 3, so your reasoning says that 3 is a spin-off.
Your previous post was vague. The way I understood "Halo 3: ODST is not part of the mainline Halo games" is that it's a side game that's part of the canon, but not part of the Halo 1-3 storyline. That's pretty much how I view the Prime games, including Hunters.
For the purposes of this discussion, here's the terminology I'm using: Main Series = Metroid 1-4 and Other M, Prime Series = Prime 1-3, Hunters. I'm not asking you to agree with it, just acknowledge that this is what I mean to avoid confusion.
Hard for Prime to be referenced in the other games since I-III came out before it. There is no evidence there are spin-offs, and I would not consider them spin-offs at all. They are more in-line than Other M.
Hence, "I suppose that's the problem with interquels." Besides, it's not that hard. It's called planning. However, acknowledging that the Prime series was not planned beforehand, why put it in the same canon? Due to poor planning, the Prime series fucks with established facts. The Prime games could have easily been an independent series and I wish it was so it could be free of the confines of the Main Series. If the Main Series and the Prime series don't reference each other, neither benefits from being in the same canon.
The Prime games are not more in line with Other M because Other M specifically references previous Metroid titles, namely Metroid 2 and 3. The Prime games make no direct plot references to the main series. The Aurora Units are suggestive of a link, but no direct relation is made. Therefore, it's one sided. Other M had a perfect opportunity to bring it full circle and didn't.
Sakamoto did not direct the Prime games, so it's wrong to claim he direct every main entry.
I don't consider the Prime games to be main entry titles.
Kojima created the Metal Gear series and given full charge of it. He doesn't do stuff that pisses off the fans of the series (he does things that annoy non-fans though).
Sorry, you're wrong. Example: Raiden in MGS2.