The list at the link above is a "request" list - not entirely representative of what actually airs on KOST.
For a 48 hour rolling list of what has aired on KOST, see link below:
http://mediabase.com/whatsong/whatsong.asp?var_s=075079083084045070077
A little harder to look at since it only shows a few songs per page and requires continuous "next page" clicks - but runs a bit farther back - is from the station's website:
http://kost1035.iheart.com/music/recently-played/
Similar to LiteFM in NYC, their gold is for the most part 80s-based with a few 90s-00s-10s sprinkled in.
At least in LA there is sister station KBIG to pick up the more recent titles (as part of the cluster strategy David E mentioned).
In NYC the newer "gold/recurrents" are spread out among competitors WPLJ and WNEW-FM (also mentioned earlier in this thread).
KCBS-FM and KRTH do sprinkle in some alternative-leaning tracks - due to the heritage and influence of KROQ with those songs
in the market 25-35 years ago plus Kevin Weatherly being the long-time PD for KROQ and KCBS-FM.
I know that the Mediabase link I posted may or may not be entirely representative of the playlist. But, it does show that KOST is noticeably softer for an AC station in 2017, even compared to other iHeartMedia ACs, which are notoriously light and 80s-heavy. Speaking of iHeart, in Houston, which has a younger median age, the local AC KODA (Sunny 99.1) is noticeably heavy on the 80s while being relatively skimpy on the 90s/00s (or even rhythmic tracks in general), and sometimes playing soft tracks which other AC stations in most of the country, let alone the South, stopped playing altogether as they pursue a more contemporary, uptempo sound. In contrast, Atlanta, another major metro in the South, has a less-softer, more-contemporary AC in WSB (B98.5).
ACs from other companies like Cumulus, CBS, Entercom, Cox, Beasley, etc. aren't as soft as the ones from iHeartMedia. Although, KOIT (owned by Entercom) in San Francisco has adopted the heavy on the 80s/less of the 90s & 00s mantra, oddly enough.
I thought that adult contemporary stations like KOST & KBIG are successful because they hardly have any direct challengers, which explains why there is a split in the mainstream AC ratings in places like Chicago (WSHE & WLIT) or a split in the hot AC ratings like in Washington DC (WRQX & WIAD) and New York (WPLJ & WNEW). And is it indeed odd for KBIG, as a pop/Hot AC station, to play and/or test alternative songs when a much more rhythmic sound in hot AC is desired (as evidenced in places like New York, Washington DC, Atlanta, and Charlotte) in this climate, perhaps to sound more appealing to millennial professionals. Even Birmingham has a more uptempo hot AC than Los Angeles, and Birmingham is a conservative market.
On another note, KIIS-FM isn't as resistant towards non-rhythmic tracks as before, given that they have known golds from artists like Blink-182, Linkin Park, and Imagine Dragons, and they played songs like "Wish I Knew You" by The Revivalists for a while. Ten years ago, KIIS-FM practically avoids non-rhythmic songs unless they chart extremely high; they basically sounded like Power 106 during that time.