After playing some more of Musou 3DS when the stages get more difficult, I actually think the 4 character thing is handled kind of badly. The problem is that when you're not playing as the characters, they are sucky sucky AI who get beat down. So like I switch from my main guy to someone across the field and play as them for a few mins doing some mission, then next time a mission shows up with my original guy I change back to him and don't notice this his health which used to be full is now at 1 combo until he is dead and I get combo'd once and the mission fails. I think if you're going to do multi-character I'd prefer the other characters to just not really exist when you're not using them so they don't take damage.
Also I think the other problem with Musou 3DS is it's hard to tell what's going on in the map. Like instead of there being a main objective, it's more about constantly doing missions, but the missions are just all over the place both literally and in objectives. I got one mission where I was supposed to stop 6 guys from entering an area from 3 directions, except only 2 guys were in the area and the other 2 were across the map. But even if I had three guys, during the time I'm stopping enemies with one guy, the others are getting past my sucky AI guy in another. It's kind of too chaotic.
I think there's definitely some good ideas in musou 3ds, but it feels pretty janky design for a musou. Like they didn't think the ideas through fully.
I'm really surprised to hear that DW7 has no mini-missions during stages. I thought it was a standard feature in musou games these days. GM3 does it really well, there's only one or two the entire stage and they're just in the corner with the mini-map and totally optional.
Btw, how long are the stages in DW7? After having all the stages in GM3 being 5-10 mins, doing 20-30 min stages in musou 3ds feels like a drag.