NTSC being 60Hz and PAL being 50Hz, there is compensation implemented in code such as shorter autorepeat delay (16 to 12 frames) and rate (6 to 4 frames), as well as gravity drop speed past level 10 (-1 frame) to keep the gameplay sort of similar to casual players.
But then details matter at these insane player levels, NTSC is 1 row every 2 frames on levels 19 to 28 then 1 frame starting with 29, but PAL is 1 row every 1 frame ever since 19, so given that frames are not the same duration PAL is comparatively harder than NTSC starting with 19 but easier starting with 29 (... provided one can survive up to that).
So wall-clock PAL gravity ends up being 1.25x faster than NTSC (but with quicker DAS: 1.5x faster delay, 1.33x faster movement), then at 19+ is 1.67x faster, then at 29+ 0.8x "faster".
Just FYI, PAL and NTSC are field based, not frame based. PAL is 50 fields per second, and NTSC is 60; a field is either the odd or even lines of the display. So that's 525i/50 or 480i/60
The NES always sends the shorter type of fields, so for NTSC you actually get a little over 60fps with the same 240 lines every fields; it's not standard NTSC timings, it's 240p60; same deal with PAL. The SNES and Genesis could optionally output interlaced video, but only a handful of games did.
But then details matter at these insane player levels, NTSC is 1 row every 2 frames on levels 19 to 28 then 1 frame starting with 29, but PAL is 1 row every 1 frame ever since 19, so given that frames are not the same duration PAL is comparatively harder than NTSC starting with 19 but easier starting with 29 (... provided one can survive up to that).
So wall-clock PAL gravity ends up being 1.25x faster than NTSC (but with quicker DAS: 1.5x faster delay, 1.33x faster movement), then at 19+ is 1.67x faster, then at 29+ 0.8x "faster".