if you find yourself using assault that often you are doing something majorly wrong, enrage's primary use is to give you a FREE 6 rage, on a 45 sec CD, considering the full rotation lasts 12 seconds, typically with 3 different variations depending on a bit of RNG with proc'ing your VT, Assault might, MIGHT be used 2-3 times during the entire duration of a 1million hp dummy parse, if the rotation is done correctly assault is never used if you look at this 500k I just linked (don't have a recent 1mill to post).
The only other filler ability typically used is Force push, seeing as that does higher damage than assault and generates rage rather than using it, and saber throw is a core part of the Vengeance rotation... so not sure where you get that from