I think I was rather unfair to hybrid plants earlier by giving the impression that cross pollinated plants will always produce weak or regressive offspring.

That is often the case because most of our garden plants are cultivars, the result of past cross-breeding to develop a better plant.  So, often a random hybrid will be a step backwards.

But it is also a part of natural selection.  A superior trait can appear by random cross pollination and with human help, or better genes, become the dominant species.

I've read that Cox's Orange Pippen apple was such a cross.  Now that plant hunters and our huge garden plant industry have brought together plants from every continent.  Some with common ancestors, separated long ago and having followed different evolutionary paths, now brought back together could sometimes produce new and still better characteristics.