I have used autoresolve in the past for an entire game to get to grips with the strategic side when going from one TW title to another as the strat side makes the biggest changes. As the battles are relatively easy as they don't really change as much as the campaign side.

The original purpose of the campaign game in all TW titles was to generate battles for the player to fight - the fact that the campaign games also turned out to be good games in their own right is a bonus!
If they actually listened to fans who want a MP campaign game they might actually have figured out that the RTS side of TW is not as important to the long term strat players as the campaign side.

MP fails in my opinion because the battles do not have a campaign context. They are once off and have no impact apart from the actual game. In which case there are many RTS out there such as Dawn of War which can be more engaging. Particulary as the amount of fantasy units has increased to the point that fantasty RTS games are not that different anymore.

Campaigns are the key to why people play TW, it is the bit that keeps SP engaging. Which if you consider the ratio of SP to MP kind of clearly indicates the import of campaigns.