Re: Avengers-rail, exactly. Universal made it clear if it traveled thru EPCOT, there would be arbitration. Why it was resort line only. I don't remember such restrictions on GotG-rail. Vaguely remember riding it to EPCOT, but that could have been another wrap.
Re: characters, they were still inside a park where guests had paid admission (albeit not the normal admission). If they outsourced Harry Potter or Simpsons look-alikes, would still feel the hammer brought down on them.