Revit really has to do a better job with its Routing Solutions.
#1 - Common sense dictates that Routing Solutions should be managed by user-defined Routing Preferences. If I set my Routing Preferences to only use 15-degree increments for fittings, then a 34.06-degree elbow should not be a part of any routing solution. This would cut down on many of the silly solutions that are generated.
#2 - If #1 cannot be accomplished for some reason, then I should be able to place what elbows I need, align the open ends of the elbows, and count on Routing Solutions to competently connect those two elbows with a straight piece of duct.
There are simply too many possibilities to be efficient. And most times none of the solutions work. I believe these two things could help.
Let's do better with this potentially wonderful, but currently dreadful, feature.