MCU actors should be allowed to play multiple characters

I don't know about that, but I don't understand why actors from other franchises are off limits. Is there a reason an actor can't be a character from the DCEU and the MCU or the Fox-men at the same time? Harrison Ford was Han Solo and Indiana Jones at the same time. Ian McKellan was Gandalf and Magneto. Sure, maybe the same guy shouldn't be Iron Man and Batman, but I see no reason why Marvel couldn't use Chris Pine for example.

I'm hoping Brolin playing Thanos and Cable tears down this imaginary wall for good.