But then you get annoying firmware providers like Broadcom who refuse to write OSS drivers for linux and a lot of work is being spent on the reverse engineering
GPU vendors have come to the realization that the in-kernel driver needs to be open-source, but the userspace portion can be closed-source. There's just really no good reason to accept a design where outdated closed-source drivers could keep you from running a current kernel. WiFi NIC vendors have for generations been moving more complexity into the closed-source firmware blob that runs on the NIC's own processor core(s), so there's no good reason for the kernel driver to remain closed-source.
Broadcom has been doing FullMAC designs for over a decade now, and that is exactly what you describe: moving all the functionality into firmware and having thin opensource kernel driver
OpenWrt accepts binary only firmware running outside of the Linux kernel address space on the wifi chip itself. This matches what upstream Linux also accepts. This works well with most recent Wifi drivers. OpenWrt does not accapt binary only kernel modules or binary only userspace applications, they are very hard to maintain if you do not have the source code.
This works well with Mediatek and also Qualcomm and most other vendors.