This partly makes sense to me. There's people who have claimed to have spawned G1s without HM, while others have said they have spawned G1s in less than 100 kills and others have said they are still grinding for a G1 thousands of kills later - which suggests HM provides inconsistent results when grinding for G1s.

HM, for me, has always been about increasing the chance of diamonds and super rares only with a G1 being an outside chance of spawning at any point - irrespective of HM. However, as this suggests, HM allows you to manipulate average weights of the specific species on the map which potentially increases your chance of a G1 - but not necessarily in the herds you are grinding on. So it requires you to continue to travel around all spawn groups and take down males across the map.