I think that both you and chez17 are listing factors that contributed to the decline of SC2. Design errors made by Blizzard cannot be dismissed.

Idra leaving the game because he hated it. Sea lasting about a week on Liquid before going back to play BW. Naniwa being forced by Alliance to play at IEM despite not having practiced for months due to Swarm Host infestation of EU ladder. Artosis pitching Starbow to prominent eSports organizations. Not to mention never ending community complaints about Protoss design. These are not signs of a beautiful game.

With Legacy of the Void alpha reveal Blizzard themselves have addressed many of existing design concerns. Breakable force fields, Swarm Host redesign, warp-in nerf, powerful defensive Zerg unit and even major economy adjustments.

You are correct, SC2 will never surpass MOBAs, but it can do much better than it is doing now.