Good post.
For me I think the problem MoS and BvS have had, that the MCU doesn't is simple... familiarity!
Everyone knows Batman and Superman, and everyone has an opinion on who they are and how they should be portrayed.
The Avengers characters however were relatively unknown – Hulk is the only character people had reference too... no surprise he's the character that's been harded for Marvel to get his own movies right!
Going forward this will be a problem for Marvel - Iron Man especially, RDJ IS the character and it will be hard for them to relaunch him when the time comes
I can see your point...they weren't known movie properties like Batman and Superman. But I don't think that's the real issue. Batman has been successfully introduced and relaunched multiple times. It has been successful (Keaton, Bale and now Affleck) because of compelling stories...or parts thereof in Affleck's case. WB/DC have a story problem. Disney/Marvel have had duds too but overall their movies have been entertaining. WB/DC simply tend to make dumb (Green Lantern) or boring at times (MoS & BvS) movies. I really liked TDKRs but parts of it were uninteresting and boring. Other parts had you scratching your head about motive and character development. I recommend everyone who is interested in the sausage making of movies watch this:
https://en.wikipedia.org/wiki/The_Death_of_"Superman_Lives":_What_Happened?
This seems to be WB/DCs ongoing problem. Too many cooks in the kitchen with different visions of what these movies should be which lead to disjointed and in cohesive story lines.
What Disney/Marvel has going for it is Kevin Fiege (sp?). He leads the big picture and keeps the whole thing on track. That's why they jettisoned Perlmutter (sp?) from the movie mix. These all encompassing movies with unifying story threads need an editor like Fiege. I thought thats what they brought Geoff Johns on board to be but that's clearly not the case. So they will continue to sputter along imo releasing less than stellar movies that will always take a back seat to the MCU.
And as you can see, I've always been a DC guy but good is good and mediocre is mediocre.