I think you're overestimating Mario's comboing potential on DK, let alone the fact he has to find his way through DK's superior range. Mario has some cute combo on many characters and unfortunately DK is no different from most characters, seriously.
Mario can't kill. And I mean this both ways. DK is hard to edgeguard, let alone KO off the stage. Mario has to work hard to get the combos going, and has to work had to get a KO. Thing is, Mario is another character that has trouble getting past a DK using Bair correctly. Tilts and Giant Punch are also very worrisome for Mario. DK can still Up throw Uair Mario at % where he dies from the Uair. DK edgeguards him extremely well. Also long as the character isn't Jigglypuff or Luigi/Samus at higher %, DK can still get a string of Uairs going. Trust me, racking up damage is no problem, let alone the fact it can simply be done patiently as Mario is trying to get instead DK's range.
Unforunately, DK can't Up B oos Mario when he hits his shield in certain parts. Lucky for DK, almost always if Mario is hitting your shield that way, he's in a position where he's going to get shield grabbed.
If Mario had everything Doc had, this would be much better for him hehe.
Wrap up: Mario can hit DK a lot but still has a hard time finishing the stock. Unfortunately on top of that... he has to hit DK first, which is very troublesome. DK can be nice and patient with his range and has solid KOing options on his side. DK pretty much just out lives and outranges Mario.
what do you mean "how do you kill with mario?" use your smashes. F-smash has range and can easily beat DK's b-air. You can u-tilt/u-smash him at many different points. His b-air is his only good ranged move, which requires DK to be in the air. Also, it is incredibly easy to edgeguard DK with pretty much every character in the game. You can take the ledge, or hit him out of his up-b, whether he goes high or low. Also, they both take about the same amount of time to kill each other, but mario has better combos for sure. He also doesn't always have to grab to set them up, whereas DK does. It's also not easy for them to grab each other.
IMO, 55 - 45 mario
EDIT:
Ok, now to be picky on other things you have said.
Mario=Doc? How so? Doc completely out performs him in everything.
Alright, you got me there. Typing error. IMO, it's 55 - 45 for doc.
Mario > Link? Mario can't kill dude. Link outranges/spams him. I'll have to elaborate later I guess.
I used to think that link > mario, but you can out camp link, by reflecting his projectiles and throwing fireballs at him. His fireballs are actually faster than link's projectiles as well and it's not like link's will beat out mario's anyway. Link can keep mario in the air really well, but mario's combo game is much better once again. Edgeguarding is incredibly easy as well. once you take the ledge, you can do whatever you want to him. Also, mario and link take about the same amount of time to kill each other. Just avoid his grab, because it's really slow.
IMO, 55 - 45 mario
Mario = Peach? Lmao, maybe back in the day. Again, how the **** is Mario killing Peach? It's also not like she has a hard time approaching/damaging him at all. Again, I'll have to add more later lol.
yes, he also doesn't have a hard time stuffing her aerials. He also outranges her d-smash, with his own and beats it clean with no clink. He can camp her pretty well and cape her turnips. They do quite a lot of damage, especially if she tries to approach with them. He approach isn't very good without them though. His f-tilt is also good for keeping her out, when she tries to approach with aerials (other than f-air, but it's slow anyway). Still, u-tilt is better.
He can also keep her above him really well with is u-tilt/u-air and is much faster than her on the ground. She has better priority and edgeguarding, but that's about it. His u-smash also kills her pretty quickly as well.
Mario vs Ganon is definitely Ganon advantage.. Tell me how the hell is Mario going to approach Ganon effectively?
first off, if ganon is trying to camp with jump back aerial, you can f-smash through it, or stuff his f-air with a n-air/u-air/b-air/u-tilt/f-tilt and potentially get a combo. Mario is much faster on the ground. He can also combo ganon well off throws on top of that. Ganon takes less hits to kill mario, but mario has a good combo game on ganon. They both have easy edgeguards on each other as well.
Secondly, mario is much faster if ganon wants to stay on the ground and can easily get shield grabbed for most of his ground moves (aside from f-tilt).