@ EL: Are you aware that Kirby's f-smash outranges and has equal priority to all of Marth's ground attacks? Also, a good Kirby will only start approaching Marth on the downswing of his Final Cutter, leaving less of a chance for punishment since the hitbox will be in front and the shockwaves will stop any ground approach. The majority of Kirby's attacks actually count as a disjoint because they involve his shoes, so his priority, while not enough to override Marth's, can actually cancel out Marth's attacks. I'm not sure which character's attacks come out first, though.
One other note: Kirby isn't as easy to edgeguard as you imply. Final Cutter, if used at the right time, will
outprioritize Marth's oncoming attacks, and airdodge->inhale will usually work on Kirby's part. From that point, Kirby can either spit Marth into the side of the stage and bair-spike (stage spiking), stick him underneath the stage where he can't recover from (stage gimping), or just Kirbycide. And yes, I do know that the first two options don't work on some stages without walls underneath the ledge.
That being said, I acknowledge that Kirby in no way outperforms or is equal to Marth, and I'm sure that this post probably won't even change the matchup to 6:4...
*Waits for comeback argument and general ridicule*