Seeing as this is marvel. I could have seen this playing out much worse. Like giving Nick Fury plastic surgery or transfering his mind to a knew body or something. Thought marvel did a much better job for this than I initially thought they would.
They had to tie the new character to the name Nick Fury somehow. If he wasn't related it would just be weird. Marvel would have done some retcon where Nick Fury wasn't Nick Fury's real name jus tthe name everyone who took the position was forced to be called by or something. Like agent Lynch from the A team, or a Men in Black Agent.
So far this seemed ot be a good transition imo.
I don't think you can just introduce a new character, and say he is this dude who has been around and is very experienced and accomplished and have him take over for Nick Fury. That sounds forced to me. And Marcus isn't the director of Shield he is just an Agent. This gives Marvel a chance to build him up. So maybe 5 or 10 years from now he can be the director of Shield.