English is probably one of the worst languages you could pick to be a universal one. But it's probably wasn't ever PICKED. It just became the defacto one.
I disagree. I think English is an imperfect but still fairly reasonable "choice".
You could argue, why not Mandarin or even Arabic or whatever, but since Indo-European languages are the most widespread language family worldwide, it makes some sense that the world language is a member of that family just by demographics. Among those, I believe English is a pretty reasonable "choice" because it's a Germanic-Romance hybrid that mostly got rid of the complicated systems of gender and inflection that are typical for the family.
Untypically for the family, in English only individuals with an actual sex are referred to with "he" or "she", everything else is "it", done. It's a pain in the arse to learn the gender of every single word in German or Italian or whatever, in English this problem just doesn't exist. Makes it much easier to learn.
Inflection, another complicated issue in other languages of the family, is almost eliminated in English. Some irregular verbs aside, you sometimes add an S or a D on a pretty predictable basis and that's it. Again, much easier to learn than the usual chaos in other Indo-European languages.
Tenses are fairly complex in English, and it can be quite difficult to get it right even for speakers of closely related languages like German. However, while it may be a challenge to get the subtleties right, a basic understanding of simplified English can be easily achieved. You can use only simple present, past and future with words like "after", "before" and "while" and everyone understands what you're trying to say.
The biggest problem I see with English is orthography. The relation between spelling and pronunciation is highly irregular in English, you have to learn both for any word because there's no reliable connection. That's a great advantage of Spanish: if you know how it's spelt you know how it's pronounced and vice versa. But then again, Spanish has those stupid genders and a lot of complicated inflection.
But in the end, this is all theoretical, because a world language isn't chosen, it emerges. Some languages vanish, others become dominant, that's how it's always been. Repressive governments/dictatorships may force the use of a certain language, but unless we'll have a world dictatorship, I think English will grow as the dominant language of the Earth, whether one likes it or not.
Is English the perfect world language? Certainly not. Is it "one of the worst"? I'm sure it's not either.