Thanks, robintodd, for compiling this list. It's super interesting to see this lineage listed out.
I distilled the list into what I think many would consider to be "the" major coaster installments--that is, big, landmark, adrenaline pumping attractions. (I also added The Beast and Top Gun to this list... )
The Racer (1972)
Screamin' Demon (1977)
The Beast (1979)
The Bat (1981)
King Cobra (1984)
Vortex (1987)
---
Top Gun (1993)
Flight of Fear (1996)
Face/Off (1999)
Son of Beast (2000)
---
Firehawk (2007)
Diamondback (2009)
Banshee (2014)
Mystic Timbers (2017)
Orion (2020)
What I see from looking at this data is that there have been three distinct surges of big coaster additions in the park's history: they were added consistently between 1977 and 1987; 1993 and 2000; and 2007 and 2020. It also looks like those coincide with changes in ownership: the transition from Taft to KECO is at the tail end of the first era, then the purchase by Paramount, and then Cedar Fair. It should also be noted that, overall, Cedar Fair seems to have made a special impact on the park in their time: all major coaster additions have been guest favorites and highly reliable. Their stretch of routine coaster additions also spans the longest amount of time compared to prior owners.
The data also shows that while Kings Island may have always catered to families, thrill seekers were never really excluded from the equation for a majority of park history. Even in those "off years" between big coasters, there have been other significant draws for thrill seekers like Delirium, Tomb Raider, Xtreme Skyflyer, and even the backwards Racer. This is on top of other family additions like the aforementioned smaller coasters, kids area renovations, the Lion Country Safari, the original Phantom Theater, Adventure Express, etc.
Overall, it's clear that the park has fared far better than many others. I also do believe that every addition we've had since Orion has been a net positive for the park as a whole. But it seems hard to not feel that there is currently an unusual and distinct lack of the fresh thrills the park has (mostly) always kept up with. The additions like Snoopy's Soapbox Racers, Adventure Port, and Phantom Theater are well-received, but in the past, there has often been a greater effort to add more extreme additions at the same time. The formula post-Orion is seemingly "one or the other," whereas the park we've been used to has often felt like "both" was an option.
We are now approaching the longest gap between major thrill attractions, not just coasters, the park has ever faced. Speaking just for myself, I do feel that gap a lot these days.