I am not misunderstanding the situation. If you omit me from a group message with our circle of friends because of the color of my speech bubble, you are not a real friend. Full stop.
The "blue bubble" just signifies someone's using the iMessage platform, and we still have multiple messaging platforms nowadays. Think of it like "Usenet friends", "IRC friends", "ICQ friends", "AIM friends", etc.
I don't know you, of course we're not friends. I addressed this in my comment. There are group chats you are part of and ones you won't be part of. Most people maintain multiple different overlapping group chats.