Would a grunge song in a major scale be still called grunge or punk (because punk has usually more energy than grunge).

yes because the scale won't matter as much. it's more based in the tone and tempo played.

Esp when there are a high number of major/melodic punk. both of pop and non pop varities.
as well with grunge.

I agree with this. You can vamp up the "grunge" on a track by having the right production style and guitar tone even if there are different songwriting elements involved. Superunknown would be a great example. Granted, there are some minor thirds in there but thanks to some major six's it sounds pretty upbeat. It sounds more like just a rock song than particularly leaning towards punk.

Also keep in mind grunge/desert rock with that sort of flavor loves to abuse riffs like these:


Those being 11's and 12's not 1's/2's of course...

Like half of Nirvana's songs are in major keys.