He does pass better than Morris, and can probably shoot the 3 better too (though Morris has been working on that and has been trusted by Kobe in some spots to hit the corner 3 -- but you can see that Morris is still shaky when doing so).
Blake cannot finish around the rim at all. No layups. No floaters. No drawing fouls from opposing bigs. Etc.
What Morris brings is solid D on fast guards -- something we have not had since.....
That helps keep Kobe, Gasol, and Dwight out of foul trouble, and helps so that Ron can guard the opposing team's other top wing scorer.
Duhon's D (like Meeks') is not great, but it is active and he is quicker than Blake. Thinking about guys like Parker, Westbrook, CP3, Crawford, etc. -- Nash will be torched bad enough. We will need Morris to TRY to slow them down at certain points in the game. Blake is actually worse than Nash, it seems, in defending his position.
On offense, I don't really see how Blake with "THRIVE" in MDA's system when he is not a threat to make a transition layup. To be a great passer in transition don't you have to at least have a credible threat of attacking the rim and scoring yourself? He can pull up at the elbow and hit on occassion. Then again, Morris is not a great finisher either...but I prefer the D and speed over all else.