What you are experiencing is common when grafting onto a large tree. Unless you remove much of the rest of the tree these shoots may not take off. Even if you make the grafts the tallest part of the tree that may not force strong growth where you want. The tree usually sends up strong shoots from the area where large cuts were made. But each tree is a case unto itself so results will vary.

You well may be right fruitnut.

I have seen what you describe when "parking" a graft on a mature tree (apple) These are still pretty young trees, This year should be thier first significant bloom (and hopefully crop).

I am not willing to cut into them too hard to push the grafts. I don't want the tree to be switched over to sweet cherry, I just wanted to get one significant branch and see how they perform.

I've not grafted cherries but with apples you can get the very best growth possible on vigorous old trees by grafting on well exposed water sprouts.

A picture would help, ...on a young tree at the tip should normally work OK...if you don't have many side branches.

Konrad your point of side branches is a good one. Both of these trees while quite young are much more bushy/heavily branched than any apple of comparable age. It could be that diluting influence is my problem. a lot of the smaller wood is coming out this spring so hopefully that will help.

If rest of tree is not putting out vigorous growth graft cannot grow vigorously. I found this out when trying to graft recently transplanted trees and also spurred up pear trees that were also suffering from early defoliating scab. With pear I put on disease resistant varieties but existing tree couldn't push grafts. I'm hoping that these grafts survive and eventually thrive, taking over trees. If this is possible I should find out this season.

The trees are fairly vigorous in themselves, and as noted now heavily branched even at present low total hieght.
I should probably done a bit more summer pruning but the take on the grafts seemed so tenuous I was reluctant to commit. It's clear now with the tape off the take is complete(whip and toung), just no vigor.

What is the opinion on the fruit buds themselves?
Remove them? pull blossoms? or let it be and hope some moderately aggresive pruning kicks things into gear by itself?

Maybe they just didn't adequately heal. Last year was the first time that I waited for plums to completely leaf out before grafting them and I got much better results than in previous years.

With apples and pears I get by far best growth with grafts just before or just at first growth.

I had heard that warm weather is the issue with stonefruit but I suspect it is more stage of development. Stonefruit grafts probably heal quicker when trees are at a plus level of stored energy- apples and pears store more energy in their wood (not as much vegetative summer growth). Of course warm weather would also help in energy storage, so maybe it's a combination of factors.

Just a theory.