Both players are highly technical and can get past pressure at times. But both of them have the same problem, they can't cope with physicality.
Santi's definitely not a liability when he doesn't have space. In fact he thrives using his quick feets to get past lots of pressure. I would have thought the "he can't tackle, he doesn't intercept" debate is dead by this season, after so many evidence of him putting good defensive work in. The description you made is actually perfectly suited for Ramsey.
Anyway while we are on this debate, how great is it to have someone like Coquelin who copes superbly with pressure as our deepest midfielder now?