I think Mantha might be a slight upgrade on Vrana in a vacuum. The fancies like Mantha much more defensively than Vrana, though Vrana is a bigger offensive threat according to the numbers.
Outside of a vacuum, I think the upgrade is bigger. Mainly because Laviolette clearly does not trust Vrana and hopefully will trust Mantha. ~17 minutes a night of Mantha is much more useful than ~12 minutes a night of Vrana. Meanwhile, I do think this sends a message to the locker room, though I don't know exactly what it is. I'll leave it up to other people to let me know if they think that message was needed.
I think the price is steep, but I also don't value first round picks like others here.
I also think this trade is going to reflect heavily on Peter Laviolette. He was crystal clear that he didn't like Vrana, so if for whatever reason Vrana becomes a superstar in Detroit I think Laviolette's decisions regarding Vrana in Washington need to be under heavy scrutiny.
Fun trade, sad to see Vrana go. But I get it, I guess.