It's an interesting point you make, and to be honest I don't dig into the iHeart classic hits stations as much as I do Audacy. You're correct about WLS, and I notice they just made a big jump in the 18-49 demo, which proves your point.
WLS-FM has slightly decreased the 70s tracks, but it seems they just increased the 80s. There are still plenty of 70s tracks in there though. I went over their playlist on TuneGenie today and saw two 90s/00s tracks - "Smooth" by Santana and Rob Thomas, "Cryin" by Aerosmith, and "Drift Away" by Uncle Kracker and Dobie Gray....and all 3 of those tracks have connections to artists who had massive success in the 70s and/or 80s. WROR in Boston, owned by Beasley, is quite similar in approach and we've seen their numbers.
This is what
KLTH in Portland sounded like at 4pm in to the 5pm hour PST today...they're a bit older leaning, but fairly typical for iHeart and classic hits. A couple of these could be stream inserted, but those pretty much match the station playlist and aren't exceptionally older or newer. #2 6+, and one of our resident experts (David E.?) I recall said the station showed quite well in key demos last year.
Guess Who - American Woman
Billy Joel - It's Still Rock & Roll to Me
Fleetwood Mac - Go Your Own Way
Beatles - Hello Goodbye
Depeche Mode - Personal Jesus
Commodores - Brick House
Def Leppard - Love Bites
Santana / Rob Thomas - Smooth
Duran Duran - The Reflex
Steve Miller Band - Jet Airliner
Patrick Swayze - She's Like the Wind
Dexy's Midnight Runners - Come on Eileen
Bee Gees - Night Fever
Mr. Mister - Broken Wings
Quiet Riot - *** On Feel The Noize
Proclaimers - I'm Gonna Be
Bill Withers - Lean on Me
Audacy's classic hits stations seem pretty top down compared to even iHeart - the 70s tracks you hear are pretty much going to be the same across all of the classic hits stations, with some exceptions. None of them are going to be playing "You Ain't Seen Nothing Yet" or "Summer Breeze" (played on KLTH in morning drive today), or the other variety of once well-testing 70s tracks still played across the classic hits format on iHeart or Cumulus stations. I'm not one of those arguing Audacy should only be playing "older music because it's better because I say so" - I'm more curious as to how older tracks are still working for iHeart, but Audacy is pushing all of their classic hits stations more recent than, say, iHeart, Cumulus, or smaller companies like Beasley. There's no denying Audacy's approach has worked for them in more markets than not, but there seems to be more at play than market and competitive variations.
To make this a bit about KRTH again, ironically, they were one of the first stations to adopt the rock lean in the Audacy stable, as well as discontinue the use of jingles (sans WCBS and WOMC I believe) and use listener shouts instead.