Yes, channels are not always best solutions for any case. There are cases mutexes are more suitable. Just choose the best solution for specified cases. Always sticking to one is not a good attitude.
We used to do a coding exercise at a previous job that was really well suited to mutexes and whenever someone tried to use channels they ended up with a much more complex solution.
Equally, there are lots of cases which lend themselves to channels really well. Waiting on multiple things at once is hard to without channels and select for example.
Yes, channels are not always best solutions for any case. There are cases mutexes are more suitable. Just choose the best solution for specified cases. Always sticking to one is not a good attitude.