Thinkman,
What is the goal of this project. You seem to be saying 2 different ways of how you want to balance characters. You want to make them all diddy level, but you are also saying that you will not change anything unless it will help a matchup. I think you need to get your thinking straight before you progress any further with this project.
First, I want to say that the diddy comment was misguided. I could have just as easily been Marth or G&W; the idea is that that is the rough level we are aiming for characters to move to.
Second, these are not two different ways of balancing characters. Saying I want people to be "similar to Diddy" is the
WHO; who gets buffed (those below), and who gets nerfed. (those above). Saying we are going to focus on the worst matchups is the
HOW; the parts of the character we are going to improve in order to get them up to that "Diddy level" r whatever you want to call it. Not only are these two concepts not at odds with each other, but they go hand-in-hand to the point that neither could proceed without the other; we have to know both who to buff, and we have to know how to to do.
If DK needs changes, as proven by matchups, then he will naturally get changes. Naturally, these changes will be selected to help him deal with the problem matchups. For example, nair angle buff might be a great way to deal with spacies if they prove to be too good agaisnt DK. Floaties a problem? Maybe d-smash could be even stronger? I'm jsut braininstorming off the top of my head, obviously real consideration would take a long time, involve readings form the DK board, watching videos, and talkign to DK mains; all after reviewing that initial matchup data.
I am by no means so good with Kirby, but as you said he has gotten worse from the changes and was already worse than Diddy in brawl. What is you logic for not buffing him? When I play as kirby i basically only use bair and fsmash so i don't know any real buffs, but I imagine it will deal with making a previously unviable move viable since you can't change throws and those are pretty much his greatest strengths.
Remember, this is a preview. It was never intended to be a candidate for exceptional balance, even if it is a good step forward on many fronts. The intent is to gather matchup data to help make educated and informed changes, taking into consideration the major metagame changes.