you only need a solid 15 fps to be sufficiently responsive to be playable. once you hit 30 or so, your animation is smooth and your responsiveness is quite snappy. anything more is just smoother animation eye candy. turns out that lower framerates (within reason) aren't bad, variable frames rates are bad.
This reads like an absolute truth, but it isn't; it depends wildly on the game. While the games you make might be fully playable at lower framerates (and might also thus be what you're accustomed to), it does not mean that translates to every other game/genre.
For fighting and racing games in particular, higher framerates are easily noticable, far above 30 frames per second.
For a chess game without fancy movements/animations, 2 frames per second would probably still be playable (although possibly somewhat annoying with selection latency).
I can't think of a single instance where a higher frame rate would lead to a worse product, but I can definitely think of the inverse.
For VR games/applications, what is considered to be usable is also much much higher, although not for the same reasons.
That said, I definitely agree with constant frame rates being very important. Companies are also starting to catch on to this, e.g. by offering optional frame rate limiters if the frame rate varies, and even in some cases options for whether graphics quality or frame rate is to be prioritized (both of which, for console games, are a fairly huge change to the status quo).