Well, yes.
The thing is, length and time you can derive from the Lorentz transform. Mass doesn't fall out of a mathematical approach, it's just (ok, not JUST) a linear constant that (appears to) scale with gamma. The energy in either case is equivalent as you say. It's just....I dunno, I just think the momenergy approach is more elegant and I'm trying to spread the feeling, know what I mean.
Anyhoo, no hard feelings here.
Cheers and shake?
et