My main beef with KOTCS is that there is a clear disconnect between older Indy's great physical shape and Harrison's really tired face in most closeups.
In other words, I struggle to reconcile Indy's screen heroics (which are on a par with any of the previous movies) with Ford's facial expressions up close.
The contrast is too jarring.
The simple fact is, Harry was already too old when KOTCS was shot.
The last movie in which he looked like a convincing older Indy is "Six days and seven nights".
Bring on a new actor for Indy V, all Harry can really do a this stage is bookend a story set before the trilogy in the timeline and shown in flashback.
This would be the perfect premise for the next movie, IMO.