Well, if one or more sorts dominate totally, then you hardly will get much fruits of the others ...

Sanguinello, I agree if the situation becomes as bad as you state. Personally, I would try to prune as little as possible, and favor of production. Take a look at Joe Real's 100 variety cocktail tree on this forum. Joe Real pretty much kept pruning to very minimal. - Millet

I read all of Joe Real already and I wished he was here in this forum still.
His contributions were always one of the best.

I have 5 cocktail citrus fruit trees. I think grafting the same types of fruits with each other will help with the lopsidedness.

One is a 5in1 multi variety that was given to me. I graft whatever variety I can get my hands on. I believe its up to 12 or so. The lime is the most vigorous so I graft mostly onto this branch.

My second one is my all Tangerine/mandarin tree.

My third is an all grapefruit tree.

Fourth is an all lemon/lime tree, mostly lemon.

Fifth is an all blood/pigmented orange tree.

If anyone is interested, I can list the exact varieties when I get a chance.

As for non citrus:

I have two 5in1 apple trees, both with different varieties, grafted 2 more onto one of them.

5in1 Asian pear tree. Grafted 2 non Asian varieties onto it.

5in1 plum/peach/apricot tree, grafted several onto it but the tree as a whole is not doing well.

5in1 cherry tree, grafted two more onto it.

I'm trying to do a cocktail mango tree but am having trouble finding scions.

I've tried avocados too with successful grafts but keep on getting die-back from the destination branches.

In my back yard I have Swingle understock with cocktail, Golden grapefruit, CaraCara, several varieties of satsuma, seedless Meiwa grafted on to it. The grape fruit definitely are the most vigorous, then the satsumas, and last the Meiwa.