A few points:
1. The topic is "best metal band of the past 20 years." I think pretty much any kind of metal will do, so quit whining about whether whatever subgenre you happen to have singled out is "true" metal.
2. Who cares whether DT influenced a particular band? They've influenced tons, to one degree or another, but it's not like the vast majority of bands that exist today wouldn't be around if not for DT. Both sides of this argument need to get over yourselves.
3. Symphony X aren't really "progressive metal." They never really have been. Yeah, there are elements of that here and there, but they are pretty much the poster children for symphonic metal. Yngwie took neo-classical-influenced metal to the extreme and put it on steriods in the '80s. SX, led by Romeo, took what Yngwie did and put it on steroids in the '90s, added in some nasty Pantera-esque guitar tone and extreme time signatures, and there you have it.
4. Speaking of symphonic metal, this subgenre really took off in the '90s, although a lot of people seem not to have discovered it until the '00s, myself included.
5. I had never listened to Meshuggah prior to clicking one of the YouTube links in this thread. I started enjoying it. Then dude started "singing" and I realized I haven't missed out on anything.
6. I had never listened to Mastodon prior to clicking one of the YouTube links in this thread. I started REALLY enjoying it. Then dude started "singing" and I realized I haven't missed out on anything.