I know we argue with each other a lot, but I have a lot of these same concerns.
If I understand correctly, this design has not been built or tested. It’s still pretty theoretical, so we don’t really know how well it would work. The general concept performed well in the BLF GT — a constant current circuit regulating power from 10% to 100, and below that it used PWM at 10 to make lower levels work. But I don’t think BLF has done that with a linear FET opamp before.
The first linear FET design, using attiny85, had issues with too few pins. It sacrificed control of the button LEDs, and it put the enable function for three different circuits on one pin. This basically makes the “PWM for low modes” useless at in-between tints like 3500K and 4500K, but, assuming it doesn’t break the USB circuit, it should still work at exactly 3000K, exactly 5000K, and exactly 4000K (ish). It makes some parts of the color space inaccessible. And it means the main LEDs would have to be at 10% power or higher, depending on tint choice, in order to function as a power bank.
So there’s a newer design, using attiny84. More pins should fix those two issues. However, it isn’t a supported MCU platform yet, so it adds a significant delay while I write a hardware abstraction layer and port firmware to the new MCU. And then there’s still the unknown factor of how well the linear FET opamp would work.
This project is already over 2.5 years old, and I’d like to get it to production soon. So I’m personally leaning toward using the 7135-based driver. It’s simple, its behavior is well-understood, it meets or exceeds the project’s goals, and it already “just works” today.
The dual linear-FET design with a bigger MCU is very interesting, and may forge a new path forward for BLF drivers… but I’d prefer to work on that as its own R&D project instead of adding risks and delays to this project.