I think in most cases, copper has to will continue to be used by professionals in preference to Hep2o. However, I don't exclude Hep2o on the grounds it is for amateur use only, that's ridiculous. The whole point is, copper is best for some types of installation, and Hep2o is better for others. You wouldn't use copper for underfloor heating for example.
It's not true that plastic fails more than copper. Who's not seen copper split after freezing or compression joints weeping years after installation let alone capillary fittings not soldered properly?
Frankly, I would not like to choose between the two. In my opinion they are different products with different characteristics that should be used accordingly.