"it has forced english speakers to become so adept at vowel-reconstruction that one could pronounce words with completely arbitrary vowels and still be understood."
This was still occurring before people were able to widely hear other regions' speakers, though.
However things like cough, plough, although, thorough, etc having different, -correct- pronunciations are due to English taking in words from other languages.
I'd go so far as to say that english is now spoken by so many people in so many different regions, all of whom can now be heard by each other on a reasonably frequent basis, that it has forced english speakers to become so adept at vowel-reconstruction that one could pronounce words with completely arbitrary vowels and still be understood.