I think they would know if they developed it as a multiplayer game or not
Sure, and you'd think that the ME3 developers would know if they made the ending based on your game choices, but you'd be wrong.
Anyway I never said the comparison was perfect, it was an analogy.
Talk about missing the point. I didn't argue against it because it wasn't perfect, I argued against it (successfully) because it doesn't work as an analogy.
The point is this game was designed as multiplayer, the online requirement is there to enforce that, I don't see how you could say otherwise.
Well, I can say otherwise because it's not true. You've yet to demonstrate any factors that support it as being "designed for multiplayer", other than the online requirement - which has already been shown to not require multiplayer, the AH, another factor that doesn't require multiplayer, and "always ready for someone to jump in", which is demonstrably false when playing a private game.
Perhaps what you mean is that it was designed primarily
for multiplayer. That's almost certainly true. But being designed primarily for multiplayer doesn't preclude having a singleplayer component - think BF3 for example.
If you want another example perhaps a private FPS match against bots?
Sure, let's take UT3. Would it be fair to say the game was designed primarily for multiplayer? Absolutely. Would you be correct if you said it had no singleplayer component? Absolutely not.