I have not seen any concrete evidence of ASUS locking down firmware. Do you have a source on this? What specific model did you buy since not all ASUS models have been as open as others

This only means you use the router for the simplest of tasks, and accept the limitations being governed by the manufacturer firmware. There’s no issue with this choice, but once you actually need the extra/advanced features and fully utilize the difference of control & customization you will never look back even for…