By mentally retarded play testers (which by the way, I'm not even saying they were play testers), you mean the mass market? As a designer, I need to take in every comment and complaints from everyone, and formulate a response on what works and what doesn't. If I can talk to close friends and let them play DW games, and they don't get it (and they're well versed in many other games), then it doesn't matter if the fans think it's easy to get: there is a gap between fans who get it, and others who don't.
Personally, there are two ways of looking at Dynasty Warriors:
1)Dynasty Warrior is a niche game and a niche genre, and Koei should embrace it (and we see this with the Orochi games)
2)Dynasty Warrior is a game that has mass market appeal, and it's just that the mass market has not discovered yet (and Troy, in a way was an attempt at that by taking more "mainstream" elements)
If you take the former, then we wouldn't have this thread: fans are more than comfortable with the game being as they are, and we don't really need to care people hating on the franchise. More importantly, if you look at some of the Media Create numbers, you can be certain that most musou games land around 300K sales, no matter how good/bad they are.
If you take the latter, however, you're stuck with our thread and the dilemma: Why do people not like DW games? What can you do to bridge that gap? If you trying appeasing that gap, what consequences does it have on the musou feel of it.
Musou has an issue of being many things to many people, and not all of it are the same: Some people identify the large cast of characters as a musou staple, some identify the battlefield management stuff, others identify the grinding and loot aspect. So where do you put the knife down when you need to change stuff for a wider appeal? I remember first playing DW6 with the Renbu system, and I thought it was interesting, and polarizing way of doing it (and in general, absolutely hated by the most vocal ones).