I absolutely agree and understand very well. The only thing they are required to tell you are your miranda rights. And they have to do it as they arrest you.
But remember? This is not being “detained”. When you are mirandized you are now formally arrested. Those two rights are now the only two constitutional rights recognized from that point on. All others have been temporarily removed until you are found not guilty.
Yes, if they read your Miranda rights, you are under arrest. However, they still don’t have to tell you why until you are arraigned.