Mostly, anything that gets broadcast on TV, and also movies, avoid using too heavy accents, because it is true that English speakers will not always understand each others accents. I've seen subtitles used for heavy accents, but this is more often done as a joke.

Speaking to real people is very different. If people you talk to have a heavy accent and do not make an effort to speak more clearly, it might very well be impossible to understand them (at least until you've listened to them enough to start understanding the accent).

Listening to a foreign language is always much harder than reading it. I can read Japanese to some extent (at least if I have a dictionary), but listening to it is much harder, except for really simple sentences. I'm pretty good at listening to English (I am not a native speaker), but watching a TV show entirely in English with no subtitles still means I have to concentrate a lot more than watching it subtitled.