> the grafting combo can alter the grafted plants epigenetically and the result can be inheritable for self-pollinated plants or having true-to-type progenies
Epigenetics Is pseudoscience and was not proven. It hangs on the reality that there are external methods for modifying DNA like virus and plasmids, but this is a really small, non functional and normally negligible part. Most accidental mutations and modifications are non heritable and discarded at gametes level.
If rootstocks would put any trace of DNA on the grafted plants, all new orange cultivars would be hybrids of Citrange at this moment, all new pears would be quince pear hybrids, and all roses would be of pink color. This is obviously not happening.