Mendez was not given good sound. The only serious record companies in the 50s and 60s who turned out records that still sound superb today were RCA and Mercury, EMI, and Decca/London. Decca/London put their emphasis on classical recordings. Mendez was considered "popular" music and was not given benefit of the better microphones and equipment. His very earliest recordings were done in mono only and the recordings are rarely better than mediocre. The "Singing Trumpet" is slightly better recorded than the others. The Almeida/Mendez recording is OK too, but Mr. Mendez was suffering from severe emphysema which made playing extremely difficult for him. His legendary breath control was now gone.
Here is a link to the Trumpet Herald's Mendez forum which is run by Dave Hickman, who is one of the better trumpet players on the planet and is a Mendez expert.
View Forum - Rafael MÃ©ndez: Trumpet Herald forum
There you will find some insight on Mendez.
I completely disagree with your findings, but you certainly explained your reasoning. I respect that.