As a non native english speaker, I don't agree that english has relaxed pronunciation rules. People have trouble understanding english coming from, say, spanish, because english has around 20 vowel sounds whereas spanish has 5. So for any spanish speaker starting to learn english, the differences between, say, cut & caught in spoken english are not evident at all. And this is going to happen to any speaker jumping to languages with more vowel sounds.
Furthermore, cantonese is a bad comparison to english because it's a tonal language; i.e. the inflection of the word changes the meaning. So on top of having to learn more or less vowel sounds, students have to struggle with a fundamentally different way to conceptualize language.
> English is everyone else's second language because pronunciation is not a big deal
That is not true. English has become the lingua franca of the day because England & America have dominated the cultural and commercial global market for centuries. The adoption of lingua francas has nothing to do with how easy it is to learn a language (after all, this is incredibly relative) and more with how international trade and history have shaped a region. For example, in the late bronze age the lingua franca was Akkadian, a semitic language that would've been pretty tough to learn for, say, indoeuropean speakers like the greeks.
Having moved to an english-speaking country because my husband is a native english speaker, I find that even with the language immersion is difficult. Unless you have a very particular hobby that allows you to connect to other people, it's difficult making friends because of the cultural differences. And even though at this point I'm so fluent in english I've written and published fiction stories in it, it's still a difference that can be felt - imagine being barely fluent or speaking barely a few words.
That's not 'more relaxed' pronunciation, it's a set of different accents (not a phenomenon unique to English). People don't arbitrarily mix and match between them, and any particular accent preserves enough vowel distinctions to largely keep different words distinct. That's different from a learner using the wrong vowels randomly.
The underlying linguistic issue here is that when we're young our brain trains itself to classify speech sounds into categories based on the speech we hear around us -- so sound differences that matter in our native language(s) go in different buckets, but differences that don't matter in that language are ignored. That makes it harder to learn a different language later where the bucketing is different because our brains naturally ignore sound changes that should be significant, and need retraining.
Furthermore, cantonese is a bad comparison to english because it's a tonal language; i.e. the inflection of the word changes the meaning. So on top of having to learn more or less vowel sounds, students have to struggle with a fundamentally different way to conceptualize language.
> English is everyone else's second language because pronunciation is not a big deal
That is not true. English has become the lingua franca of the day because England & America have dominated the cultural and commercial global market for centuries. The adoption of lingua francas has nothing to do with how easy it is to learn a language (after all, this is incredibly relative) and more with how international trade and history have shaped a region. For example, in the late bronze age the lingua franca was Akkadian, a semitic language that would've been pretty tough to learn for, say, indoeuropean speakers like the greeks.
Having moved to an english-speaking country because my husband is a native english speaker, I find that even with the language immersion is difficult. Unless you have a very particular hobby that allows you to connect to other people, it's difficult making friends because of the cultural differences. And even though at this point I'm so fluent in english I've written and published fiction stories in it, it's still a difference that can be felt - imagine being barely fluent or speaking barely a few words.