That's where you're partialy wrong in assuming.
While yes, most everyone can communicate in written english, quite a lot of countries in EU have rather low standards when it comes to understand and communicate in verbal English. Other then Brittain, Sweden, Norway, Denmark and Finland are at the top when it comes to communicating in English. Most other countries have little to no education in verbal English, and thus have a hard time undesrtanding and speaking English. That's why it wouldn't work as well in European shells and on a multilingual level.
Just because they can write and read English doesn't mean they have extended knowledge in actually speaking and understand it. Hell, there's quite a lot of English dialects I have a very hard time understanding, such as Spanish english, French english, scottish English, hell, even a few American and Brittish accents are hard to understand at times.
Considering the huge ammount of different accents the English language have, linkshells with people from several nations can missunderstand eachother at times, or simply not hear what the other is saying properly, which can cause people having to repeat what they said.
While yes, Vent allows people to fast and efficiently communicate with eachother, the downside is that it can cause missunderstandings, several people talking at once, thus not hearing eachother, or people simply not understanding said accent etc.
Adn that is where text communication have its benefits. It is hard to write in accents, most everyone can read/understand it, and you can scroll up and reread it if need be. The downside is, naturally, that you can't play and type at the same time, and it takes slightly longer to get your message across.