I have found out that mutex solutions are more maintainable and amendable without big redesigns compared with channels or RCU.

Consider a simple case of single producer-single consumer. While one can use bounded channels to implement back-pressure, in practice when one wants to either drop messages or apply back-pressure based on message priority any solution involving channels will lead to pile of complex multi-channel solutions and select. With mutex the change will be a straightforward replace of a queue by a priority queue and an extra if inside the mutex.