considering how long amd has been using 32nm its not quite as simple as saying, bad for margins. contracts and yields and other factors, could make its cost them less to produce some of the last 32nm with a bigger chip vs early 22nm parts as a smaller chip.

for A6 vs i3 your still limited by tdp when it comes to such things. a full 4000 could be running at lower clocks to maintain 25w or less tdp
in anands test the battery life of trinity vs hd4000 was about equal for their gaming (it was only mentioned in the text briefly, but it would be good to see how it really performs per watt in gaming)