It's true, we haven't seen him shooting those powerful shots in a while. But I think it's more circumstantial, not being able to catch it properly or going for accuracy instead of power.
I'm having a hard time believing though that he has physically lost strength. It doesn't make sense to me, he even broke the power records in the test when he joined.
There was one freekick in the beggining of the season where he had a strong shot, it also went directly at the keeper. Then there are all his other free kicks where you can't really tell if it's heavy since they hit the wall.