Correct Stuart ,
One really great unit was the Yamaha Stomp which actually had multi tap delays and other delays which could be configured as series or parallel. If the Zoom is series design it means the echos add together and so a compromise has to be done to get a reasonable result by reducing echo levels and using ears. These days I use the Stanley Baby Blue as at £150 it is the best and cheapest option and fits nicely on the pedal board. That's about the cost of these Zoom units and you get correct echos fir Shadows music. I still own a Zoom G3X and an Hall and Collins though. I also have Eccas eTapH2 but find the Stanley Baby Blue is perfect for my pedal board.
I do not understand why effects manufacturers do not consider it to be a great idea to put 4 to 6 tape delays in a multi head config and allow users to specify levels and timings surely it's a straight forward thing to offer?