Of course it can. But, the mixbus is just another (inexpensive) tool that can give certain projects/mixes a special character that would be hard/highly unlikely for me to achieve using x1/x3 and the standard plug-ins.
I have not actually used mixbus as a recording tool as it does not currently support midi or Vsti's but I have exported bounced tracks from x2/x3 and imported into mixbus and using the stock EQ was able to achieve mixes that were better than I am capable of using x3 alone. But that is just my personal observation.
I can't tell you that it will speed up your workflow because it probably will not but, it will give you an inexpensive tool that may provide you with special finished character that X3 probably would not provide alone.
I really believe that mixbus is just getting started and I wanted to get in on it while the costs were still low. I think it has great possibilities as long as Harrison continues to support it.
I also use the Mackie MCU and extender and am hoping for an update soon that will support this. I do miss using the control surface when using mixbus.