We don't need a mirror to breathe

Correct observation, though I heard only bits and pieces in some videos, YouTube, etc. 

I remembered Dr. M.B., Maharajapuram, somewhere in the late 50s; MS, Semmangudi; and GNB all together rendering that in MA. So as far as lyrical faults are concerned, no one teaches the exact meaning of at least those songs they learn (they need not know Telugu, Sanskrit, Kannada, or Tamil).

Still, while musically rendering, there could be some excuses given for shortcomings if pauses for breathing or getting immersed in musicality (raga) are dominant. 

Even many legends and stalwarts (I don't want to name them) have had some shortcomings in lyrics, but the overall raga bhava-imbued rendering compensated for that, but here many were reciting them as Vaipaadu (multiplication tables). 

Most importantly, classical Carnatic music in general and the compositions of Mumbai Murthy in particular are not meant for ghosti ganam, as the emphasis is more on melody, manodharma, and individual improvisations if the artist (vocal or instrumental); they are not meant for a big harmonic orchestra of collective rendering. 

Carnatic music is rarely rendered (unless old or taught too many compositions) with notebooks or sheets with notations hoisted on a pedestal. 

Even those who know thousands of critiques just render them from memory. 

We don't need a mirror to breathe, close the eyes or open the eyes and see something, listen to something using our ears and mind, open the mouth (unless sitting in a dentist's chair) and taste something, or touch something and feel it. 

Classical Carnatic music's raga-based melodies are meant to permeate into the five senses and also sensitize the five senses in mind, heart, and soul. It is sublime in that aspect. Great itihasas, epics, and certain novels and stories too follow this pattern. See the slide below. 

However, I would be failing in my duty if I didn't mention that Dr. Balamuralikrishna's school, M.S. Subbalakshmi's school, T.N. Sesha Gopalan's school, and D.K. Pattamal's school pay immense attention to the perfection of pronunciation of the lyrics in any Indian language.