For playing Link on Smash 64 for the past 20 years, I think I'll show up here to give my opinion about these suggestions.
Link is pretty darn close towards being a menace against everyone else in the cast, so buffing him has to be done very carefully.
1. Make his ariels faster and less laggy when not Z cancelled
All of his aerial attacks, except Forward Aerial, have 3-5 frames of startup, so they're pretty fast in their own right. If you're talking about F-Air though, which has 14 frames of startup, I'd reduce it by 2 frames; it may not sound much, but it'll help a lot in the long run.
2. Make his grab hitbox a bit bigger in order to make it more worth using
3. Make his grab a bit faster
I honestly think that the 3rd option is better than the 2nd one. All tether grabs are slow due to their range. If I were to change it, startup should be 6 frames faster, and its recovery after attempting should be reduced by 20 frames. Compared towards everyone else's grabs which are very fast, this change would still be slow, but would be used a little more often, and not as lack-luster than before.
4. Make his dashing speed faster
He really doesn't need that change, unless you're talking about his running speed, then I humbly agree. Link is tied with Ness for 3rd for fastest Dash Speed being 68; compared to C. Falcon's 80. His running speed is pretty mediocre at best actually, being tied with Jigglypuff for 3rd worse Running Speed with a whopping 42, compared to Mario's 44. I honestly believe that he should walk and run faster but not his dash. Increasing his Walk Speed to be the same as in the JPN version (0.37 -> 0.4), while his running speed should be increased from 42 to 50 (tied with Yoshi); this should help with his mobility issues while keeping the feel of him being slow due to so many tools he has on him.
5. Make his jumos much higher
This one is interesting, cause his jumps got shortened due to his gravity increasing slightly (3.2 -> 3.4), when comparing from the JPN version to the NTSC version. This is just enough so that Link can't reach to the side platforms on Dreamland when jumping sideways, cause jumping sideways would cause you to jump much shorter than neutral jumping. Reverting his gravity values back to what it was in the JPN version should help alleviate multiple problems, such as his recovery in general.
6. Make F-tilt and F-smash faster for easier K.O
His Forward Smash is very fast on startup, so I'd have to agree on it being able to KO better, so changing his KB values (not DMG%) so that it feels the same at KO-ing as in the PAL version. His Forward Strong is pretty good at KO-ing, yet is a bit sluggish in terms of speed, so reducing its startup by 3 frames should be suffice at doing its job.
I agree, as he's pretty slow at pulling them out. The entire duration of pulling out a bomb is 44 frames. Reducing it down to 34 frames should be enough to pull out a bomb when he has enough space to do it, especially in Dreamland.
Not sure what you mean by "faster bombs." Sorry.
He did get nerfed from the JPN version to the NTSC version where the overall damage from the bomb is 2% weaker, 1% if thrown downwards. So with that said, I agree for it to be reverted.
I don't think he needs this, as the boomerang can go quite a ways as it is. In the JPN version, he whips his bent bread-stick like it's baseball.
11. Decrease hurtbox to compensate for his size
His hurtbox sizes are close to how his model is like. My only guess as to why this suggestion is that his non-dominant arm that holds his shield is sticking out more than it should. Making those hurtboxes when not attacking intangible should be enough to fix that said issue.
12. Turn D-air into meteor smash
Again, I don't think he needs this. If he does though, then I'd suggest that the first 6 active frames should be a Meteor Smash.
13. Make his recovery actually viable
See my opinion on #5 of your post, as it's related to it. His Up-Special is a powerhouse, when it comes to damage and KO potential, so it'd make sense for him to have a bad recovery move to begin with. The reduction in its gravity values actually increases this moves jump height in the process, so his Up-Special doesn't need any changes.
See my opinion on #5 of your post, as it's related to it. The gravity change is already good enough.
15. Make his shield protect from projectiles
This one is difficult to think about, but I'm just gonna bring it down to just my opinion towards your 11th suggestion. Other than that, use your attacks or projectiles to destroy your opponents' projectiles, and you should do just fine.
16. Make his air speed faster
See my opinion on #5 of your post, as it's related to it. The gravity change is already good enough.
17. Give nair a longer lasting hitbox/animation
Neutral Aerial Attack's hitboxes lasts on frames 4 - 29 throughout its 39 frame duration, so I don't think he needs this change.
18. Make his sword longer
His sword got 5% shorter, and made his sword look like plastic, when transferring from the JPN version to the NTSC version. And I agree, his sword's length should be reverted.
19. Make his up-b meteor smash
I need an explanation about this change, cause I'm not seeing anything good from it
20. Idk I don't have one for 20
My suggestive ideas for #20 is to increase his weight to be the same as in the PAL version: 0.96 -> 0.9, or 108 -> 122; as this will help his endurance very heavily, including his recovery even more as well. Changing his weight isn't gonna affect him as much as there are TOD combos everywhere in this game.
The other idea is shorten his Jump-Squat frames by 2, as he has the slowest startup when jumping in the game, reducing it to be even with Yoshi should be enough to help with his juggling capabilities.
Overall, my opinion is fairly close towards this post, but I honestly think that, even though he's 11th on the tier list, Link isn't that far behind actually. He mostly needs fixes in many areas while buffing a few things in the process, and he should be good as new.
