High-speed-drive increases gears dramatically!
This means: On a push of a button all existing gears are increased by a factor of 2.5.
Therefore, it's not just a "nice-to-have" gadget, that gives some additional gears - no - it's more than a doubling of the number of gears, mostly without any overlap!
You can imagine the effect as follows: if you have a small and compact 27 tooth chainring installed, on a push of a button this chainring acts like a 2.5 times bigger one, means a 67t. chainring!
If you compare this range 27 -> 67 with a triple chainring, you can easily see, that no triple chainring set can offer such a wide range.