Rock music doesn't chart anymore.
*mainstream* rock music was buried 10 years ago
If by *Mainstream Rock* you mean Rage Against The Machine, Limp Bizkit and the like, you're correct. And it couldn't have died soon enough for me.
All kidding aside, my definition of *Mainstream Rock* - and most, if not all, Generation Xrs seem to agree with me - encompasses what is today four rock radio formats: alternative rock, mainstream rock and (Adult Album Alternative) triple A and, of course classic rock. You rarely, if ever, get them all today on one terrestrial radio station.
But I do agree with your point that there is still a lot of great Rock music out there, including much of the same type of Rock that Dom and I grew up with. But the methods of locating it all have changed.
In short, you're assertion of a Golden Age of music - even confining it to Rock - has merit, IMO. There is literally something for every sub-genred Rock taste. I'm certainly not going to turn up my nose at Modern Rock. Plus, many Rock bands are staging recording comebacks. No reason Led Zeppelin shouldn't be one of them.