> All the other manufacturers have really really shitty BSPs in comparison,
I disagree.
The NXP (i.MX line) and the TI (am62x) and the STM32 MP1/2 all have good mainline support.
What you say is true of most of the Chineese chips and of mobile chips but if you go with mainstream suppliers targeting the industrial / automative markets these days mainline Linux support is good at the SoC level. At the SoM level some are better than others but it's not that hard to pull the approriate DTS into your mainline kernel build even if it isn't already upstream.
RPi is probably better for hobbyists but that's not due to the mainline status but a community more in tune with hobbyists than the more industrial products.
I've built professional embedded Linux systems based in i.MX5/6/8 and STM32MP1 with mainline based BSP rather than vendor stuff but have only ever used the RPi for one off tools.