I'm afraid no amount of explaining will help on this. Statements like this:
They just generally sound like a power metal band covering death metal songs to me.
...have always, and will always strike me as nonsensical. The idea that there is some sort of objective checklist of features which defines what sub-genre a band is really irritates me.
And specifically the "trying to be a [insert ridiculous sub-genre here] band" part of the original comment. I know you've already tried to explain that, but it seems what you really meant was "they share some characteristics with another band or band(s), whilst not sounding exactly the same as said band(s)". But for some reason, you've slapped some genres on to the argument and turned that into something negative. As if the fact that they happen to straddle 2 of your neat sub-genres somehow shows that they've attempted and failed to be one 'kind' of band, and so are in fact another 'kind' of band.
Do you see what I mean? :lol:
I really don't 'get' the whole thing.