No, that’s not an advantage, nor is it even a characteristic. Bus routes tend to not change very frequently, especially at their cores. Things get very expensive relating to startup costs to create limited-service alternate routes (created via pandering, to boot) that end up fizzling out due to lack of demand or inability to recoup costs to a certain requirement. Furthermore, bus routes that change too frequently tend to drive away passengers due to the confusion it creates.
Also, BRT special routes are just as fixed as rail. Not to mention more expensive to maintain than rail.