Probably only your main and friend team can defeat even normal enemies on maps, so I'm not going to ask if you've gotten full clears on everything.
Every main story mission 3* clear gives you a flower gem. Most give affection items as well except for the final map of each chapter, which gives a 3* girl. Both of those rewards are better than a chance at some gems that might give you a decent equipment. Plus, going back will let you strengthen your weaker characters and give you more teams that can fight.
I auto-setup my first team for raid bosses and so my friends can use my strongest 5 characters: http://prnt.sc/av6lpn
But what I use for clearing maps is: http://prnt.sc/av6n49
I'm confident in any of my teams defeating non-boss enemies, so I'm more likely to get 3* clears, and I have a helper who is typically 5k to 10k stronger than my "average" teams if there are extra boss fights on the map.
Currently cleared all main story missions up to 10-3 with 3 stars and waiting for my girls to take the right turns to 3* clear 10-4 lol.