And that's why I think Kirby/Diddy is even.
While I agree that the only thing reliable in a match-up discussion is the pure character differences (anything else is player-based), I don't necessarily agree with your interpretation of those differences. Basically I think you've over-simplified your conclusions. I could do the same by doing this:
Number of Jumps (Kirby): 6
Number of Jumps (Diddy): 2
Kirby's fastest attack: frame 3
Diddy's fastest attack: frame 3
D-throw Damage (Kirby): 12%
D-throw Damage (Diddy): 9%
Jumps: +1 Kirby
Fastest Attack: +1 Both
D-throw: +1 Kirby
= Kirby has the advantage in this match-up.
Now that I have posted my silly example, I will go into specifics.
RE: Kill Power
Kirby's 'safest' KO option will always be his B-air until he has his opponent at a high enough percent to KO with his U-throw (151%*). Since B-air is also Kirby's general spacing move, it will usually be staled out and thus will usually not be likely to KO until about 160+%. Using F-smash, Hammer, etc. is usually a poor option in any match-up, but they become exceptionally poor options in the Diddy match-up due to the spacing that Diddy creates with bananas. In general, Kirby will only be landing F-smash with hard reads (punishing Rolls/Dodges/Air Dodges/Tech Rolls/broken Shields).
*this damage is the
'base damage', that is to say without DI on Final Destination.
Diddy's KO power is significantly less than Kirby when comparing maximum knockback from any given attack, but when only comparing 'safe' KO options, Diddy has a clear advantage. Diddy's F-tilt, U-tilt, F-air and U-air all become safe and reliable KO options at about the same percents at which Diddy gets KO'd by Kirby's 'safe' KO options (about 150%). The difference here is that Diddy has many and various KO options while Kirby only has his B-air and U-throw, both of which are iffy on how well they can KO (B-air's stale moves modifier and U-throw requiring either an overhead platform or significantly higher damage percent on Diddy). Additionally Diddy has the ability to move in with a Glide Toss and hit-confirm a banana-slip into a D-smash or F-smash for even more KO power. Kirby's banana set-ups are much weaker given he only has JC-Item Tosses and no significant Glide Toss.
For reference, here are the KOs that Gnes and Chudat got on each other (that set at APEX 2010).
Diddy's KOs on Kirby
F-tilt: 155% (R1
2:24)
F-smash: 132% (R1
4:06)
F-air: 137% (R1
6:36)
U-air: 135% (R2
1:20)
D-air: 143% (R2
3:38)
F-smash: 161% (R3
1:48)
F-smash: 188% (R3
4:40)
U-special: 110% (R3
5:45)
Kirby's KOs on Diddy
U-air: 174% (R1
2:51)
Gimp: 135% (R1
6:00)
B-air: 165% (R2
3:57)
F-smash: 121% (R2
5:03)
SD: 162% (R2
7:08)
B-air: 137% (R3
2:03)
B-air: 164% (R3
4:48)
Notice the variety of moves used to KO with Diddy: 6 of the 8 KOs came from different attacks. With Kirby we see 3 of the 7 KOs coming from B-air alone, and that's being lenient considering the Gimp in R1 at 6:00 involved a number of B-airs, and the U-air was only after 2 consecutive B-airs failed to KO Diddy at 152% (fresh/sweetspot) and 163% (2nd-hit stale/sweetspot).
Just a note, many of Diddy's KOs used banana leads and none of Kirby's used bananas.
RE: Gimping Ability
Kirby gimps Diddy's recovery about as easily as Diddy gimps Kirby's recovery, the thing is that Kirby has
more opportunities to gimp Diddy's recovery than Diddy does in return. When Kirby's recovering, Diddy is generally going to be setting up his banana game on-stage, or he already has it set up and he's just looking to get another hit on Kirby when the opportunity arises. When Kirby gets Diddy off-stage, it usually results in Kirby having a good position to hit Diddy out of his recovery and doing so on Diddy's U-special will usually result in gimping the stock. The only downside of this is that Kirby's B-air will send Diddy in a upward angle which refreshes Diddy's Side Special in a favorable trajectory as well as gives him another chance to use U-special.
Even though Kirby has 5 jumps, these do not refresh, and Final Cutter is IMO a fairly vulnerable recovery option (easily edgehogged with abusable start-up and a predictable recovery plus notable landing lag). When Kirby gets hit out of his jumps, he's going to have to resort to using a Hammer swing to get himself back to the stage and then go for a Final Cutter to make up for any lost vertical distance. This is about as bad of a position to be in as it is when Diddy is forced to use his U-special. Like I said, though, Diddy will usually be content with not going off-stage which results in Kirby getting to the ledge almost all the time.
RE: Priority
You can compare smashes to aerials to special attacks to whatever. In the end what matters is that Diddy's banana beats pretty much anything Kirby has. Any whiffed aerial from Kirby or any aerial that hits Diddy's Shield is a prime target for a Glide Toss -> Banana. The same goes for any ground-based attacks with the exception of a Grab. Any approach from Kirby is pretty much a disadvantageous risk. This is not to say that Kirby cannot approach Diddy, it's just obvious that approaching with Kirby is much harder to pull off than Diddy's side of things. Kirby must first navigate past Peanuts and perhaps bananas before he ever has the chance to go for that Aerial (or for a Grab, or feint, or whatever else since a blatant Aerial attack is pretty easily beat by Diddy).
Banana in hand > Kirby's priority.
RE: Range
Kirby has next to nothing at long range until he gets a banana. Diddy can and will use bananas more than Kirby and better than Kirby. Diddy also has Peanuts which aren't a real threat, but they're still an advantage at long range no matter how you look at it. Yes, Kirby can get Peanut Popgun from Diddy's hat, but... lol, Inhale.
Diddy's long range > Kirby's, this is even more so when Kirby doesn't have a banana.