Poland is bigger than the UK but nowhere near twice as big
And about half of Poland has no native speakers at all
And how do I define correct? By what is the easiest to enunciate and to understand.
To each his own. I'd rather appreciate some redundancy, which would make up for ambient noise and such. I wouldn't say that producing three difficult vowels instead of one simple is sloppy.
With the speed of Polish you exaggerated a bit. Maybe it sounds like that to you.
Geographic location. England being on an island means that it has less exposure to foreign influences throughout history
Looks plausible, but somehow doesn't prove in reality. USA is a huge country, and US English was constantly under pressure of all European languages, yet they say the Americans have preserved the archaic English pronunciation.
I have another theory about the accents. English is rather vowel-oriented, as compared to Polish, and vowels are easier to shift than consonants (or more difficult to keep in place). You can say 'better' or 'be'er' with glottal stop, of course, but it's still quite easy to extrapolate. Now compare 'like' and 'lake' in various accents, out of context, and you are in trouble. At least I am, not being as finely tuned to local nuances.