It's usually the Mike's responsibility to cover the vertical, just like it's the Sam's responsibility to cover the TE. Pierce had trouble covering anyone with speed last year and he knew he was slowing down, thus the weight loss for last season. It still didn't help him. I see the difference in the Tampa 2 as to where the Mike drops back in a pass recognition.
I like the safeties in cover 2 as they can split the field on the deep patterns. The trouble with last year was that the SS stayed in or bit on play action too often, leaving the FS on a huge Island by himself. If Phillips was healthy and played in that situation last year, most of the fans would be calling for his head too.
The Giants can employ a cover 2 in passing situations where the SS drops back while our corners play man and not a zone coverage. There will be press situations, man situations and there will be zone situations all based on down, distance, the size of the playing field, the score, the time on the clock and the team they are facing. It's all built into the playbook.
Let's give Coach Fewell the courtesy of actually developing his own refinement of an NFL defensive strategy before attempting to label him or his aspirations.