RDJ himself is not the problem, he is a great actor with enough range indeed. It's how Disney is playing this that's cause for concern. Do they bet that by 2026 Iron Man will have faded in people's memory, maybe? Who knows.

Personally I believe that it would have been better to go with someone else for that part. I may be wrong but I am certainly not alone in feeling this way, judging from comments on social media or forums. We'll see, I guess!