[native_samples]

Nobody thinks that, but:

1. English is an unusually compact language. If you watch dubbed movies you will notice that the characters often have to talk extremely fast compared to the original and much dialogue is rephrased to be simpler. They can't refilm the sequences so in languages that take more words, the dialogue must be simplified.

2. A lot of people won't get dubbed versions anyway, so they'll be watching it as a foreign language.

[stavros]

As a non-native who watches everything subtitled because that's what everyone does, we have no problem following complex storylines. We have a language and competent translators.

[native_samples]

And that's why I said "nobody thinks that", indeed.

Nonetheless, you seem to be fluent. Lots of people around the world speak some English but aren't fluent, don't get dubbing or subtitles into their own language for every film (or do but way late and they don't want to wait), and some of those people could in fact struggle to follow complex dialogue or might misunderstand idioms.