Well, I aspire to be one that doesn't suck for a start.
Seriously though, even though I'm not sure I'd want to be a pro at this, I couldn't see myself as a master of one. I listen to so much different shit and see myself as someone who'd like to work with metal bands as much as I would post rock bands, avant garde stuff, alt/pop rock, post metal and drone doom or whatever.
Then be able to tailor sounds to suit those different genres and bands. Recto sounds for a death metal band, but why not experiment and get some fucking weird hand built amp made specifically for sludge metal, so that it forces you to experiment and get a different mindset and get into the zone for the genre? You know, shit like that.
also have an appropriate mastering job for each.
Sure, brick walled fuckery is probably okay in tech death, but I'd fucking hate to hear a post rock band, which as a genre is inherently very dynamic, smashed to shit. Ideally none of the stuff I'd do would be any louder than say, Riot! by Paramore. Any louder than that and I don't think it's necessary personally.