The RPi3 was old hardware when it was released. It been pushed impressively as far as it will go, push it too far an it will overheat.
It needs a pretty specific 5.1V 2.5A power supply, is slower, does not support hardware decoding of 1080p / 4K HEVC, does not have proper Hardware deinterlacing and cannot do 4K or HD audio passthrough.
It cannot Hardware decode everything you throw at it like the AML S905's can do.
There is also no fast eMMC flash storage & it shares its Ethernet with a USB2 bus. No onboard IR receiver as well, so you cannot just unpack it out of the box and use with an IR remote.
Unless you are connecting all sorts of external Hardware peripherals that need a modern Linux kernel and modern driver support a $35 AMLogic S905(x) box really is superior for LibreELEC.