Raspberry Pi has some closed-source broadcom boot firmware which some folk get upset or uptight about, but unlike Rockchip who pay lip-service to upstream support and still have closed-source blobs and NXP who hide their entire ecosystem behind an NDA/paywall they openly provide A1+ support for their boards and the software ecosystem around them (both the open and closed-source bits). Pi devs have also been funding a lot of upstream development for their hardware too; because their own resources are limited and time-to-market counts so major things like mesa have been subcontracted to people with the knowledge and expertise.
NB: LE has fairly terrible software support for all the (now dated) Amlogic boards you mentioned. Rockchip support is reasonable. Allwinner is the best of the three. RPi4 still wins the best supported board medal though.