As someone who operated marine VHF ("bridge-to-bridge") professionally for years, I'll say that these recordings sound perfectly intelligible. I imagine ATCs and pilots have a similar culture of "get the point across as fast as possible, but not so fast that it is no longer unambiguous." Especially airband, where everyone in each area tends to guard and use a single frequency.

This is all captured by civilian equipment on the ground. The stuff the ATCs themselves have access to is much better.

You do need a bit of time for your brain to get used to it.

It reminds me my favorite pilot story https://youtu.be/ILop3Kn3JO8

Did we listen to the same recording? It was perfectly clear for me...