I think that's being overly optimistic. The flaws of these clubs will only be magnified in Europe. Liverpool will probably leak goals. Chelsea and Tottenham will need to add quality depth to truly compete in Europe, and Tottenham will need to prove themselves. United and Mourinho are complete question marks.
Liverpool I could see playing tight games and just not being able to score enough to go through. United similar.
I don't think United, even with a couple additions over the summer, is really close to the elite teams in Europe, but the way Mourinho manages, seeing them blown out would be surprising at least in terms of final score line. IIRC they've only lost one game by more than a goal this year. Granted I think they'd get fairly well dominated in terms of possession and chances, but be able to keep from being scoreline embarrassed.
Chelsea is an interesting team as I've said before. Could go either way this summer depending on additions and subtractions.
Spurs need to prove they can win when it matters before I bother putting much into the quality of their side.
City is City. They're deeply flawed, but if everything goes right for them they have the raw talent to go head to head with most teams.
TL;DR is that if 5 English teams make it, I could all 5 bombing out before the knockout phase, but at the same time a team like Chelsea, City, United or Liverpool getting a decent draw and making it to the quarters or something wouldn't shock me.