The people who needed to learn the M777 likely overlap significantly with those who need to learn HIMARS. Seems to me dumping a bunch of equipment at once in a country that is not familiar with operating or mantaining it all at once probably would not lead to good use of that equipment.
If you want to call it a mistake, then the mistake was not supplying this stuff years ago.
If you want to call it a mistake, then the mistake was not supplying this stuff years ago.