CMOT70: It's a MOBA. What does the "O" in MOBA stand for? It has a single player component, but only a very small one. Probably no one should be buying this game for the single player stuff anyway. It is an online multiplayer game first and foremost.
Ok then, but why then does it even have a single player component, if it is so tiny and irrelevant to the rest of the game and no one could possibly want to buy the game for it? What does that insignificant(?) single-player part add to the game? Nothing?
I wish games would be clearly either single or multiplayer games, not trying to be both at the same time for no good reason. While it used to be normal that single-player games had a multiplayer part tacked on, to me they usually felt quite separate from each other. Quite often the multiplayer maps are completely different and separate from the single-player maps, the gameplay itself may be quite different (e.g. the single-player part has a campaign and a story while the multiplayer part doesn't) etc.
Of course there are also the co-operative etc. gameplay modes (where you can play a campaign with your friend, both on the same side), but there I don't see why it should require always-online
unless you are indeed playing with someone else.