Apart from what you say about exposure (which is true), I'd say that written English is much easier than spoken English for most (if not all) native speakers, for several reasons:
- If you don't understand a sentence the first time, you can read it twice (or as many times as you want), and this very often helps as a non-native speaker - sometimes you misinterpret a word and this throws you off, but reading the sentence again clears the misunderstanding. It also can help deducing the meaning of an unknown word from context, etc. Of course in a video call you could ask the speaker to repeat, but this isn't functional if you do it often, and can make the non-native speaker feel ashamed of slowing the conversation too much, especially in work environments.
- This one only applies to related languages, but it's much easier to deduce the meaning of written words from other languages. Take the word "subtitles" in your text. Any Spanish speaker could infer that it is equivalent to "subtítulos" in Spanish, because it's spelled very similarly (Levenshtein distance = 2). But the pronunciation (/ˈsʌbtaɪtəls/ vs. /sub'titulos/) is very different (Levenshtein distance = 5).
- If you still don't understand a word, you can look it up. Or even hit Google Translate. Good luck with that in a video call.
- Written language is reasonably standard. While there can be some regional variation (color/colour, lift/elevator and so on); you get rid of all the diversity of accents which can be a huge deal for a non-native speaker.
Seriously, speaking as a non-native English speaker (at a quite good level now that allows me to speak quite comfortably, but obviously I went through all the stages of learning...) the difference between texting and phone/video calling when you're a non-native is enormous. The latter is like an order of magnitude more difficult.