Like all chile, the relative spicy-ness depends on where the plant is grown. More capsaicin is developed when grown in hot, dry climates like the desert southwest.
Some areas with moderate weather develop chile that are essentially elongated bell peppers.
That used to be true years ago but NMSU has worked with the farmers in NM for many years and they have actually come up with new varieties that are very different. More flavor and more heat if you want it, any hot with an X in front of it can very well be hotter than a jalapeno. Within varieties it does depend on rain/watering- temperature, things like that do give some variation from year to year in the same varieties- last year the hotter ones weren’t that hot but most years they really are.
Hatch green chile is great, but I get just as good green chile from Diaz Farms in Deming, in fact they have excellent chile. Deming is closer to me by far and I have never been disappointed.
The flavor is why NM chile is famous, no comparison to any I have ever had from CA, TX, or AZ (unless they grow NM varieties) and people that have only had canned Ortegas are always surprised that these are so different.