Wouldn't it be better to, instead of dropping gun control, invite candidates into the party that don't support gun control, but support other key Democratic priorities to represent redder areas?

The simple fact is that you can't drop gun control if voters want gun control. Thats what makes it a wedge issue. If party leaders start dropping gun control from the platform, they set themselves up to be primaried by people who want gun control to be in it.

It wouldn't be all that effective either. I think you underestimate how divisive race and abortion are. I would say they're much more divisive than gun control, particularly since staunch gun advocates are a  vocal minority, whereas abortion and racial issues are more evenly divided. Guns weren't even a focal point of this last election cycle and Trump actually passed some gun control measures with very little pushback.