I'm not saying we are, but modern Alternative is far from Rock in sound. Alt-Rock is a sub-section of Alternative. Could that be because of the dominance of Alt-Rock for the past few decades?But both formats are under the marquee of "rock" and rock has been on a decline for the last 20 to 25 years among demos under age 35 to 40.
Alt is highly fragmented. There are subsets within the Alt banner. AAA is eclectic, and appeals today to mostly 55 and over.
We are not in a rock era.
As for Big, my personal take is that it's a blend of big hits from what was WAAF, New 97.7, and a sprinkle of what usually makes up Jack-FM in other markets. On my drive home today, it jumped from Weezer to Tone Loc. Only station where I've heard Metallica's cover of Turn the Page and Madonna in the same half hour. I actually use Big as my go to when I'm driving with my family, as we never agree. My wife and kids want Kiss 108, where I prefer either WZLX or WGIR.