Listening to RT on the air is not the best way to learn it because you will hear very little compared to what you are required to know and much of it will be incorrect, so you begin by learning all the wrong things.
I agree that there's a fair amount of bad R/T around, and you should not use those bad examples in your exam or real-world flying.
But R/T is a language on its own. The speed is sometimes twice the normal conversation speed, there's static on the line, people are stepping onto other peoples conversations, there's loads of callsigns in use, people are making very short (and sometimes clipped) radio calls which hold a very precise meaning, and you've got to interpret all these phonetic alphabet letters. It takes a while to get "tuned" to it. You can try to get tuned to R/T while also trying to keep an aircraft in the air, while an instructor is trying to talk you through the next exercise and you are spending 150-200 UKP an hour, or you can try to do it at your leisure, for free.
I bought a 2nd hand scanner for 40 euros or so, and spent literally dozens of hours listening to the R/T of my local airport (Schiphol). Even though that's 99% IFR and my subsequent flying was in the US, VFR, I was already "tuned" to hearing R/T and it was just a matter of learning different calls. I think I was confidently handling the radio on my fifth flight or so. To the amazement of my instructor.