You are very right 2D . Point taken. This was made for TCAS.
But there is unfortunately a difference between the book and the reality :
For instance in the glider communauty, not so many machines are SSR equipped, but even when they are , they do not put it on permanently as the current Becker empties the batteries in a few hours, they normally keep it for entering class D ( enough of those since the 1st of May !)
Something else not possibly widely known : this radar info service is based on a Secondary radar image only.