Who's they? I don't recall seeing V-Moda mentioning that the M-100 were neutral. Reviews I've seen of the M-100 often mention they're far from neutral - in fact, if anything the treble may be neutral but still a bass heavy headphone. W.R.T. the word "better", that is mostly subjective as what one listener deems "better" doesn't necessarily apply to the next listener. Each person has different tastes, and in my case I have too many - depending on what I'm listening to, depending on my mood at the moment, etc. It's not even static.
Anyhow, as this is a M-100 Master thread, thought I'd add some preliminary thoughts of the M-100 Master.
I have a refurbished M-100 but I believe it's close if, not the same as the original M-100 so don't pay too much attention to the "refurbished" term. The M-100 Master seems to have cleaned up the sound quite a bit compared to the original M-100. The Master does sound a little more U-shaped, but not void of mids. Before I get into the bass and trebles, I feel slightly deeper U-shape gives wider soundstage perception, and due to the wider soundstage, the bass seems to be punchy with more room for reverberation. It's textured nicely but doesn't sound as woolly as the original M-100. The treble seems to have more sparkle and more air, again I feel due to the perceived U-shape wider staging.
However despite the wider soundstage, the imaging goes deep and has headroom for the music to breath in the virtual space it has created. Mind you this is still a closed pair of headphones therefore it wouldn't compete (not does it intend to) with open headphones.
Whilst all the V-Moda full sized cans (from M-100 onwards) have the V-Moda house signature, they do vary subtly. I find the Wireless editions to have a lighter bass presence to both the M-100 and M-100 Master. The Wireless has a somewhat fuller fleshed mids but the Master's bass has a perceived tighter punch. I find the newer M-100 Master to be the most emotive of all the original M-100, CFW prototype, CFW II Apt X, and CFW II Codex. The Wireless series would probably be for those who want a little more mids in the V-Moda house signature.
I'll spend more time with the M-100 Master for a more fully fledged review and subject to change the more I listen to them!!