I think Link is really underrated by most people. We have a local Link here that is learning quickly, and this character is just clearly really strong.
Link's "infinite" isn't an infinite at all. Proper (S)DI breaks out pretty reasonably, definitely a major case of videos against training dummies being overblown. What IS a big deal is that Link's jab confirms into pretty much anything, especially against non-floaty characters (like as Rosa I wiggle out of stuff, but even mid-fall speed characters like Sonic just get caught). If Link hits with jab, he can very easily turn it into a smash in most situations. That's fundamentally really strong.
Link's normals are just the best out of any of the sword characters all around. His tilts are all safe on block if he spaces correctly (and remember ftilt is a viable kill move at realistic percentages; he can threaten with a disjointed kill move that can be spaced to be safe). Utilt in particular is a super good move, just protects him in a way that very, very few moves in this game protect any characters. His swing patterns and sword length work together well to make him extremely high priority in effect, tends to easily beat out attacks from the non-sword characters and even does pretty well against other disjoints in this department. If this turns air to air, his ridiculously long tether attack ("zair") comes into play; it just beats stuff. He also hits like a truck; his moves just do so much damage and knockback.
Link's projectiles are great, honestly probably the best set of projectiles in the game outside of the Villager or maybe Mii Gunner. The Boomerang (side-2) is fast and good and leads into stuff, does everything you would ever want it to do really. All the versions of his bow are kinda bad IMO, but it's not awful as an option. Bombs are of course incredible, and he has so many shenanigans with them (our local Link main learned this tech for "soft throws" where he can throw them and have them not blow up; it's really annoying). Between the bombs and the boomerang he can set traps for days, set up for his normals really well, and just give himself insurance in every situation (if he has a bomb in hand or a returning boomerang, he's pretty safe from heavy punishes).
The only really bad things about Link are that his attack speed is kinda bad, his physics are combo bait, and his grab game is poor. The first part is kinda offset but the huge pay-offs from jab and the safety of his disjointed tilts; that turns him into a character who collects heavy reward from mid-speed moves which makes his attack speed behavior very similar to Rosalina (and this is a very good thing). The second part is offset by the implicit protection offered by the boomerang and bombs interrupting stuff; Link actually has ways to mitigate his risks even if he's easy to combo. The third part is what is probably the biggest long term downside; he has a slow and super unsafe on whiff grab that has poor rewards when he hits with it (though he does have all sorts of clever ways to set up for it). Link seemingly has no useful grab combos or chases, and while his uthrow is a passable kill throw, it's not really very special.
I compare him to Toon Link, and he seems obviously better. TL has better mobility in exchange for less range and way less power. This mostly makes Toon Link just annoying; Toon Link runs around annoying his opponents but struggles to finish stocks, and even for what kill moves he has, Toon Link has few ways to set up for them. Toon Link's shorter range means he's a lot more realistic to challenge than Link, and while I think Toon Link attacks somewhat faster than Link, his attack speed is still pretty poor in the grand scheme of the game. Toon Link has the same type of lousy grab, somewhat helped by his killing bthrow but also less range than Link's grab for all the same sloth (and honestly fewer ways to set up to land the thing). Toon Link's projectiles are really cool when you go custom on them (Fire Arrows and Short Fuse Bombs are both massive shenanigans), but I'm not sure they're actually better than the more straightforward and good options of Link. I just can't see giving up just how plain solid Link's pressure and pay-offs are for Toon Link's harassment if I were wanting to pick one or the other. I don't think Toon Link is a truly bad character, but I'd probably tier him as lower mid while Link I'm pretty sure is somewhere in the high tier (he's not top but I'm pretty sure he's high, somewhere between 15th and 20th if I had to guess).
As per the Project M comment, I have no idea as I've never played it very seriously. TL in this game though feels like mostly a worse version of what he was in Brawl, and while he was seriously slept on for the entirety of Brawl, being a worse version of that isn't a great place to be in this game while Link is just plain solid all around in ways that really aren't like Link has ever been before. I believe in Link, but it is true I haven't played a TL on the same level as the Link I've played (or to nearly the quantity) so maybe TL has some hidden virtues I don't know about. Just on the surface, he doesn't make a believer of me while Link has definitely convinced me.