Hybrid vigour or heterosis with mixed breed dogs such as Labradoodles

Various contentions have been put forward in the dog world by some, (eg those against mixed dog breeds), that 'hybrid vigor' is allegedly not possible (for example) when breeding mixed breeds such as Labradoodles (ie mixed breeding of purebred Labradors and Poodles) as it is alleged that hybrid vigor is only possible with mixed breeding of unrelated animals (eg horse and donkey). However, that is not correct, and the benefits and nature of hybrid vigour or heterosis in mixed breeds such as Labradoodles has been known of some some time.

It should be noted that it is well regarded and recognised that hybrid vigour or heterosis effect is 'strongest' or 'highest' in the first generation of progeny produced from the crossing of the two purebred breeds, such as in Labradoodles. That is, when the two parents are purebred (eg Labrador Retriever and Poodle) and are crossbred, their progeny or offspring have the most hybrid vigour or heterosis effect. And this first generation of progeny or offspring are commonly referred to as the F1. And the next generation F2, etc, etc.

If, for example, you were to then breed an F1 progeny to another F1 progeny, then the hybrid vigour or heterosis in the progency or offpsring produced would be significantly lower than in the F1 generation. And the further down the generations you continue (eg F2, F3, etc), the hybrid vigour or heterosis continues to diminish to the extent that it is insignificant.

Some breeders, for example, of mixed dog breeds such as Labradoodles, even further minimise hybrid vigour or heterosis by 'back breeding'. For example, they may breed an F1, F2, etc back to one of the original purebred breeds (eg Poodle). And may even deliberately continue this practice, in attempts to 'strengthen' a desired characteristic in the offspring or progeny (eg the soft curly coat of the Poodle).

However, not only would this significantly reduce and/or remove the hybrid vigour or heterosis (which is one of the main advantages of mixed dog breeds such as Labradoodles), but it would be producing offpsring or progeny which are basically just more and more Poodle, and less and less Labrador Retriever. And if that is what is truly desired, then why not just breed Poodles in the first instance? Rather than creating a mixed breed (eg Labradoodles), which initially has significant benefits from the hybrid vigour or heterosis, but which is gradually reduced or removed through the back-breeding etc?

I have provided various extracts, links etc below that relate to hybrids, and to hybrid vigour or heterosis. And hope that these may assist with the understanding etc of hybrid vigour or heterosis.

Firstly, in a New Zealand government publication(1):

"What is a hybrid?

A hybrid is an organism resulting from a cross between genetically different parents. Hybrids can arise from crosses between closely related species (interspecific hybrids) or by crosses between different types (subspecies, varieties, cultivars) within a species (intraspecific hybrids).

Hybridisation occurs naturally, but it is also widely used in selective breeding programmes for both plants and animals. The mule is an interspecific hybrid between the horse and the donkey, bred to combine some of the favourable characteristics of each parent. Intraspecific hybrids often show