i2c slaves usually responds with ACK. But maybe rockchip hardware i2c doesn't check this. Of course, if there is no VDD to the controller, this would have to be investigated first.
Otherwise, just throwing some ideas here:
1. It might be a problem with hardware i2c. You could use software i2c to validate this assomption. By keeping i2c4 disabled and configuring i2c-gpio instead (example template here). Using i2c-gpio, you should see if controller doesn't not ACK in dmesg.
2. May be an issue with the led controller identification. For example, some magicsee-n5 boards have the fd6551 chip but use brightness commands of the fd655 chip. You could try setting compatible to "fdhisi,fd655".
In anyway, it would be easier to start from a known working configuration. Since you don't have an OpenVFD vfd.conf, would you mind sharing the Android dtb from the original firmware?