Half the drivers in the Amlogic 5.4 codebase pre-date modern kernel frameworks so they don’t use them which means you need hacked versions of e.g. ffmpeg/gstreamer to match them (not upstream versions). Amlogic’s codebase also has little concept of backwards compatibility so for distro’s that need to support a wide range of hardware you will only ever get half the devices working. Older devices (not that old) will need 4.9 to be useable.
TL/DR: Linux 5.4 doesn’t mean anything when the driver code is forward ported from the 4.9 BSP which in-turn was forward ported from the 3.14 BSP which in-turn was forward ported from … 