「そうですね。」 is honorific. In this case, "ね" is often used when agreeing. By using "ね", you can also express familiar feelings. The part of "だよね" in the sentence "そうだよね" will be used for casual conversation. It is a way of saying it to someone's friend, lover, family, or person younger than that person. And "だ" is like "is" of the Be verb. "よ" is a casual feeling. "ね" is like saying "Is that right?" Feeling that someone is asking someone is able to obtain consent. And it is feeling that someone is checking whether it is correct or not.

”そうですね” ・・・is polite. ”そうだよね”、”そうだね” are casual expressions.