On the numbers......
Ericsson has played 4 years in North America. Year 5 hasn't started yet. In that span he played 2 more or less full seasons in the NHL. He was drafted 291st (LAST overall) and he was a forward then. His last season stats: 74GP 3G 12A 15Pts 8+/- 87PIM 89SOG Not bad for a 3rd pair D.
Do you know what Pronger's (2nd overall pick) 3rd NHL season stats were? 78GP 7G 18A 25Pts -18+/- 110PIM 138SOG
So it took Pronger - a surefire top pick - more than 3 years to learn to be an NHL defenseman. (And that would have been his 7th year playing pro or quasipro hockey in North America, counting juniors.)
So cut Ericsson some slack. You can't teach size, but it appears that Detroit's management believe they can teach Ericsson everything else he needs to know, and fairly quickly.
He's played in North America for 5 years. First season was with GR in 2006-2007. They've been exclusively "teaching" him either in GR or up with the Wings for 5 years. Fairly quickly??
Pronger was also 20 years old in his third season....not 27! His third year in the NHL was 1995-1996.
At 27 he statistically should be in his prime. If what we've seen so far is any indication of his prime, then he is way over-paid! Flat out.