You know, I know my friends were being supportive when I came out to them, but it felt really defeatist to be met with some version of "we know."
For me, at least, it really sucked to muster up this courage and stress about how my friends would react to be met with "Oh honey, we knew for a long time" or some version of that. To me, it wasn't comforting. I know it's well-meaning, but I think the better phrasing is closer to "that's wonderful, we have always accepted and will continue to support you."
Because you understand that people coming out thought they were hiding it well. Whether that was true or not, your response shouldn't be essentially calling them out on being horrible at their cover-up. Some might be okay with that, but I certainly wasn't. I didn't quantify it at the time because I didn't have the understanding I have now. But I can tell you that I would have preferred a version of my statement. However, I also don't expect it from my peers when I came out at the end of high school.
I still appreciate their gesture, though. It was really tough being questioning in the late 90s. Social media was basically Livejournal, and there wasn't really a lot to go on with external support. As out as I am, I'm still "non-confirm" closeted to select members of the family. I don't care if they know, I just won't acknowledge it to them. Backward religious, they're only going to cause issues with my mom, it's not worth my time. Those family members can fuck off.