I do agree with you for the minimal effort but I wouldn’t blame Blizzard as much as you do. For me, seasonal content is free content for the game. Sure, I appreciate when they give us a lot of it (not sure they ever did once) and I am disappointed when they give very little. Even this season, when we didn’t get anything, I wouldn’t be as harsh as you are.
That being said, if they want players to keep coming back at the start of the next seasons, they will have to do better.
Where I share you point of view is for VoH expansion. Blizzard didn’t do the bare minimum for a fully priced Xpac.