Oh for sure, i totally agree there, communication is the base of any relationship, even more so with a D/s dynamic.
Without being able to communicate on the long run a relationship will be hard to maintain.
Learning how to communicate and how to voice wishes and also concerns, how to be clear but also to listen to the other person if needed is an essential skill.
One thing i would add though is that this is also true for a sub, a sub that is unable or unwilling to communicate can be as disastrous on the long run
I do agree with your statement.
I would add that it's just as important for a sub to at least attempt to clearly communicate in return. Communication is a two way street and if it isn't a dominant may feel that they're speaking to a brickwall and the relationship will crumble.
Much like a regular relationship one party asking "are you okay" and getting an abrupt "I'm fine" in return doesn't allow for changes to be made.
Even as adults we make mistakes and may not know where the mistake was made unless it's communicated to us.