Yes E has played well. But Kronwall has played poorly this year from a defensive stand point, which makes E look even better. He is playing on a top pair, but he really is a 3/4 not a 1/2 Dman.
The real question with E is, can we afford to keep him. He is a UFA after next season, and the market is 5 million per year. Is E worth it? That one is a tough choice. We do have 4/5 young Dman pushing for time: Kindl, Dekeyser, Lashoff, Smith, and Sproul. Maybe this summer is the time to flip him for a top 2 line forward-something we don't have.
Sproul has yet to play a game at the AHL level, let alone the NHL level. What makes you think he will be pushing the big club anytime soon?
Sproul, Oulette, Backman, Jensen, Marshall, McKee, Nedomlel, etc, all light years away from playing any kind of role in Detroit, IMO.