...it must be infinitely better than the USA pattern joining procedure which involves a 45° turn against the circuit direction in the mid-field downwind position.
If you think about it sensibly (have you ever flown in the U.S.?) it's a far better system, where you can survey the whole circuit as you approach, and been at the same height can generally spot traffic against the sky as opposed to looking down on it from an overhead join and then descending onto a position where there could be traffic.
Also, everyone knows where you are going to enter the pattern with the 45° system, as you said yourself it's the mid-point downwind. How is that difficult?