Powell is averaging pretty much 10 and 5 in 19 mins at 53%. That's pretty solid. If Sydney weren't so ridiculously stacked, he'd be playing more and averaging more. This is a guy whose been an end of the bench type for the majority of his NBA career. He's not a young guy with potential, and he's not a legitimate NBA starter level player, he's a role player. He's also been out of the league since 2014.
Blake is seriously struggling, though. He's playing like a guy with nothing left to prove, who is pretty much here for a paid vacation during his semi-retirement. Which is basically the case, when you've got a guy whose spent 13 years and almost 1000 games in the NBA.
People see these guys like David Andersen, Steve Blake, Al Harrington, and expect them to come in and dominate, like they would have done at 28 years old in their prime. In their prime, they were playing big minutes in the NBA (or Europe) and earning multiple millions of dollars. And now that they're in the mid 30s, they're well past their prime and getting a contract wherever they can, before their career inevitably ends.