I'm a little confused about people saying it's just skill and that a Link main will do better if they don't play Link. I can confirm that is not how it works.
There are a select few matchups (and they are largely playstyle dependent) where I will do better with not-Link than I would with Link. This isn't because of a lack of practice with not-Link, it is because I am pretty generally bad with not-Link when compared to Link. Link's moveset let me develop a play style that works for me. Link isn't just "worse Fox", he is a completely different character with completely different things he can do.
The entire thing about options and better options is false. Link has options that other characters straight up do not have. Nobody else in the game has the boomerang, or even a boomerang equivalent. Link puts out a hitbox that lingers and he can control where it goes. Boomerang slingshotting is fucking awesome and something nobody else can do. The bomb is also very unique, but Peach has turnips that are similar (though they don't explode for extra hitboxes, making them easier to swat). Link has 3 projectiles, each one doing something different (the boomerang returns, the bomb explodes, the arrow makes you lose), and he is probably the best character for battlefield preparation. Link with a boomerang in the air and a bomb in hand is in a very strong position.
Some characters do have moves that are straight up better than Link's equivalent, like Marth's fair compared to Link's fair, or Marth's ftilt to Link's ftilt, or most of Marth's generic attacks compared to most of Link's generic attacks, but Link still has totally unique options.
Link's main problem is he does not have a safe answer to certain solutions like all the top tier characters have. Fox and Falco have a "this beats everything you can do in a shield" option in their shines, so they can be super aggressive and bank on their moveset to prevent it from being punished. Peach has huge priority for her defensive game and float canceling when she needs to approach. Sheik has her entire moveset being really, really strong. Marth has great range and fast moves to make use of it. Jigglypuff has the bair.
Link doesn't have an obvious strength anywhere, giving him no go-to strategy that he can apply to beat things. He has good range on some moves, but those are all slow. He has high priority on some moves, but not THAT high. He has projectiles, but they're slow and can't be canceled.
Link also lacks reliable combos on some characters, which is part of the problem. Even if he does use the right option, he doesn't get rewarded as much as others.
Link has a janky move called the spin attack that allows him to get the occasional stupid low percent kill. You can sort of combo into the jank at times, but not anywhere near consistently.
If you say Marth has a better recovery than Link you're crazy. Marth can't survive half the edgeguards Link can, and has the only recovery in the game that can be defeated by light shielding. Jigglypuff has a hard time edgeguarding Link, that's how crazy cool he is.
Edit: You need to go Zora Tunic all the time, just in case you get sent to Termina.