As I have said in an earlier post that MK had the ability to reach high notes but could not sustain at that level for the any length of time. Contrary to what many think Mukeshji too had a high range and was excellent at bass. But did not or could not experiment at high levels. Lack of experimentation is the inability of the voice to maintain at such a pitch for a long period of time. Most singers who try and do this end up getting shrill . This is what sets Rafi apart from other male singers. Rafi when reaching high pitches could not only maintain that pitch but his voice continued getting better at that level which is why he could experiment with different notes in his songs when singing at a high pitch.
Rafi had the ability to maintain a bass voice and has showed this in many of his songs. Infact he had the ability to sing in a bass voice and reach a very high pitch at the same time.
Most singers experiment with their voices at their normal range or with lower notes because they know their voices are suited to that level. Experimentation with higher notes is very difficult and requires excessive training.
SPBalsubramanya made a comment one time that when he listens to Rafi he doesn't even feel like half a singer. Such was the ability of that man to reach different levels which is proof of the fact that the majority of male singers consider Rafi to be their idol.
In 'O Duniya Ke Rakhwale', the original song was set at a very high pitch that is very hard to replicate. SPB made a comment about this song and described it as "impossible" when you hear the last part of it. The levels at which he has sung this song requires a singer who can scale all notes efectively and maintain that level. When Rafi sang this song at a concert in 1979, in Bangalore which I attended he brought in a new raaga into the song and made up his own tune for the part "Mehal Udas" which was very mind-blowing. Rafi had such a deep knowledge of classical raaga's that he was able to do this. The original of this song is very very hard to replicate and only a rare talent such as Rafi can come close to singing this song.
Yes, undoubtedly Rafi Sahab was the greatest of all. I have that version of Mahal Udas....he is fantastic. This is what singing is all about.👏