I doubt Iger's prestige is going to erode as much as you wished it would.
Iger still, even 2 years after stepping down as CEO, is a Wall Street darling. Its the reason why the rumors of internal executives making bets of him making a triumphant return to save the day made news when they got leaked. While I understand some Disney Fans may not love him, Wall Street still does and I don't see any reason why that would stop just because he left.
Now I'm no fan of Chapek, but the guy has only been on the job for 2 years. Its still early in his tenure to determine his full effect on the company. He might be just what is needed to navigate these current waters as Disney continues its transition from a traditional media company to a streaming provider. Or he could be the biggest flop since Light Magic at Disneyland. Only time will tell. Personally I suspect he'll be an "ok" CEO and be replaced once the BOD determines the company has navigated these current waters safely.
Lastly you can call it cowardice to leave, but in reality it was probably the right time and right move for both him and Disney. He had been planning to retire for years and years anyways, but the BOD kept asking him to stay. So why stay this time for what could end of being 2-3 years longer while the company navigates through a pandemic only to then begin the transition. That could end up being an additional 5+ year longer commitment than what was agreed to between him and the BOD. Ultimately there is never a right time for a CEO to retire, someone will always complain it was "too soon", "the wrong time", or in some cases like Eisner that "they overstayed and they should have retired long ago". Nah, better to leave when he did and let someone else take the reigns while he helped with the transition.