They are both genocide. When you get to that level, it is silly to play the who was worse game from numbers, both are equally bad. One just had more time and different systems that resulted in greater numbers. The level of evil isn’t different, just the efficiency of action.
I think “genocide” has the specific meaning that it’s an attempt to wipe out an entire people. It is mass murder, but with an identified demographic target. It’s not saying anything about being a lesser or greater offense, but merely describing the nature of the objectives.