I seem to be missing most of your posts, so this is a little frustrating.
Love Power Metal. But I don't think I have even seen half of these.... *sighs*
MQ- Dang.. these guys are really really great. Tight galloping heavy riffs, perfect unison to add to its punch. High, mildly gravelly vocals add a great contrast that fits the sound wonderfully. The drummer is not a standout, but fits to the sound well ( and TBH, while I love insanely brutal drumming, I think that the double kick non stop stuff is getting a little overdone). I like it, because while it might be progressive, nor brutal nor fast as sin, it just captures that classic Heavy Metal/Power metal atmosphere so well, like you said, and minus all the extra trappings that every band seems to feel the need to drape on their music to stand out. I swear some of these bands are going to start throwing in kazoo and xylophone solos just to be "original" RomperRoomCore or something. But these guys seem totally content to just grab a couple guitars, some drums and go... kinda refreshing actually.
MQ2- Heavy Load is the first I know of, but I doubt they were the first.
BQ- Least important? Well TBH, I think anything beyond the drums, guitars, bass and vocals are probably the least important. Make no mistake, keyboards, folk and symphonic instruments can certainly add to and enhance and and heighten Metal, but the basis of Metal, IMO is still the traditional amplified set of instruments, backed by pounding drums.
That said.. really I cannot single out one single instrument. Any one of the primary instruments can make or break a Metal band depending on the qualify and fit of it, so I really can't say.
***Dang it..ѕтθηЭ;D beat me to it...........