Thanks, that's useful. I do understand that flatpicks are how it's supposed to be done. Depends on what I'm playing – for bluegrassy stuff I'm using a flatpick. But for example I'm currently trying some old English songs (from the Penguin Lloyd/Williams folk songs book) in a kind of cod-baroque-counterpoint way, for which I really need to be sounding the bottom and top strings simultaneously but none of the others. You just can't do that with a flatpick.

yeah, at the moment I favour using four fingers for big chords, and try to flatten my index finger or fourth finger to make it cover two strings where necessary. But I think I just need to do some serious, boring and mildly painful practice of playing nothing but barre chords until I get the wrist strength up.