Assuredly this song is what cements Rafi's status as the greatest. If you're familiar with the intricacies of music, the reason why this song is held such high esteem by singers and musicians alike is clear as daylight. The harkatein and murkhiyaan make it an extremely challenging song as is but with the added complexity of the different octaves it traverses, the song is literally out of the reach of even the most supremely gifted/talented singers. Moreover, the varied nature of the composition also adds to the singer's burden; to wit, every stanza is different in terms of scale and notes and it continues in this vein until it reaches a crescendo at the climax of the song. Interestingly, rather than the song of our focus, it was Tu Ganga Ki Mauj which wins the inaugural Filmfare Award for the best song, most likely as it is the more hummable number. Personally, I prefer this song too but the standout song in the movie for me was Man Tadpat Hari Darshan; I can listen to this on a continuous loop for hours and never grow weary of it.
I have heard Yesudas singing O Duniya Ke on several occasions, but like you said, I feel there's something missing. Indeed, plenty others have also tried and failed miserably to recreate the mood or emotional vibrancy that Rafi infused into his version. The key thing to notice in every cover version by other singers is they're singing it in a lower scale, obviously so the climax of the song can be delivered competently. In fact, even Rafi Sahab in his later renditions (in concerts, etc) also had to do the same as his voice no longer possessed the ability to hit those higher notes. However, Rafi Sahab enhances his covers by adding in extra harkatein, murkhiyaan and taans which keeps the listener enthralled. If you've heard any of the cover versions you can't help but be completely mesmerised when Rafi begins crooning the part Mahal Udaas Aur Galiyaan Sooni - it's utterly spellbinding.
Conversely, if you haven't heard it, I'd recommend a cover by Anup Jalota who sang this song as a shraddhanjali to Rafi in an album at the turn of the millennium. He does a wonderful job and his classical training adds another dimension to the song, but alas it's not a patch on the original.
I'll leave you with an anecdote concerning Yesudas and Rafi; Yesudas began his foray into the world of HFM in the early 1970s but apart from an occasional song he was finding it hard to get a big break. Rafi had returned to the world of HFM in 1972 and by 1975 was back in high demand. Ravindra Jain was working on the music for Chitchor at the time and had wanted Rafi Sahab to sing all the songs. When he approached Rafi, Rafi politely refused owing to his busy schedule and instead recommend the name of a newcomer, namely Yesudas. Ravindra wasn't convinced and continued to press Rafi but to no avail. Ravindra took on board Rafi's suggestion and invited Yesudas for a trial, which went splendidly and so the album went to Yesudas. Upon release, the songs of Chitchor became a national sensation and Yesudas finally becomes a part of the HFM fraternity. Yesudas goes on to win several awards for Chitchor including the National Award and as they say the rest is history.
Yesudas holds Rafi Sahab in the highest esteem. In numerous interviews and stage shows, he refers to Rafi Sahab as his guru and the benchmark for all other singers to aspire to..
https://m.youtube.com/watch?v=VMEhM1kFyKg
Anup Jalotajis version of O Duniya
https://m.youtube.com/watch?v=DoBjlRHKHfw
Rafi's live version; skip to four minutes in for the Mahal Udaas part
