That's interesting that you say this as I use classical and flamenco techniques on my ukes, and classical and flamenco guitars. Finger picking makes up at least 90% of my playing, even on my steel string. The D'addarios sound very stiff and don't give me much sustain at all. They're dull and dead to my ears. I've tried quite a few packs of these because I was determined to like them. I do have a "beater" uke and flamenco, but I've only used these strings on my high quality instruments. My Sceptre sounds like a cheap thick laminate with these particular strings on it.
Brittle is the best word to describe these strings, IMO, like they'll shatter at any moment. I also think it sounds like an instrument's true sound potential is blocked by these strings. I can hear it when played and it usually sounds like something is missing from the sound, even when the most talented musicians are playing their custom instruments. Just my opinion though.