Its not the end-all that English is that language, but I think its fair to say that anywhere in the world atm English might be the closest to a "universal language".
I for one would rather stick to English, until a better alternative "proves" itself in the "marketplace of ideas".
As for the main argument about the phonetics, I think most languages have this problem, for instance in Germany every region has its own nuance and dialect, but the common one is "High German".
Same thing in English, and I would argue (even as an American) that our common version is "RP English or BBC English". If you can speak in this dialect, not only will (almost) everyone understand you, but speaking it also comes with a hint of "Respect", as its not so easy/common to do.
Is it not possible to consider that part of the English languages perceived disadvantages as a universal language could be also perceived as an indirect advantage? In that learning its grammar and structure is fairly easy (Barrier to entry is low), but perfecting the nuances of its depth in precision and pronunciation is fairly difficult.