Two bands that arent old school or even "metal" but are relatively newer are Bigelf and Kyng.
Bigelf is more prog-based but has alot of Sabbath, & Floyd influence without being contrived. They started in the 90's but didnt get much traction until the 2000s. Think they've disbanded sadly. Their CDs arent easy to find, but if you want to check them out I suggest starting with "Hex" circa 2002-2003 maybe. Saw them in a very small theater in 2009 or 2010 and they were awesome.
Kyng have 3 CD's out, all are good but their first "Trampled Sun" is their best IMO. They are doom/stoner metal with a Soundgarden bent, think they started around 2010. Again one of those bands that wear their influences on their sleeve without sounding like a direct ripoff.
I personally don't like categorizing music too much, I just look at it as good and I like it or it suck and I don't. Most musicians either hate the genre label they been given by the media and consuming public and when asked to classify their music will just say we tried to make the music we like and the best music we could at the time.