The idea that you can't overcook food with the sous vide method is erroneous. Not really sure how that idea came about, probably just someone misunderstanding what they were witnessing.
I've not really had much to do with cooking vegetables sous vide, but I love playing with my Anova for cooking eggs in-shell. In fact, if I was never to use it for anything other than eggs I'd still consider it a worthwhile investment. Yup, I love eggs and I love being able to tweak the texture of the yolk to be anything from pouring cream to Dali-esque ooze. But I digress.
The Serious Eats website has a lot of experimentation on the effect of time on various proteins, not just the eggs. Well worth the read. While the appearance of red meat may not change much with a long cook, the texture will due to the breakdown of interconnecting tissues, in the same way they do with regular slow cooking.