In terms of pure raw talent is he up there with the best players to ever play the game in my opinion. Same with longevity, not many have been able to adapt and keep a relatively high level of performance into the latter stages of their career as he has.
However 168 goals and 259 odd assists in 963 games is not a world class winger output by any stretch of the imagination.
People who say he is overrated I think is massive hyperbole, or i've seen quotes saying he is lucky he just appeared when we had a dominant team. The reality is you don't get your debut at 17 years old and you aren't a mainstay of a dominating football team unless you are a really good player, which he was.
Giggs at his best would absolutely destroy the wingers we have at the club right now... Garnacho is a fantastic talent but if you were to ask me if I would take 18 year old Giggs over 18 year old Garnacho right now the answer would be Giggs everyday, this isn't even a question when it comes to Sancho, Antony etc.
So then why are there question marks about his footballing performance, one could argue inconsistency, or him never having a truly world class season like Ronaldo did for us despite Giggs' talent. I always felt that Giggs was always outshone by other players, he was the new kid on the block with the brand deals and so on when he first emerged but then Beckham quickly established himself and took all the attention, even though I think Giggs was supremely more talented than him. I don't think his National team exploits helped him either.
It's kind of hard to pinpoint really... I'm mostly going to chalk it up to recency bias though, there's a lot of wild opinions these days on how a lot of footballers from many moons ago, of the 90's and so on, just aren't that good anymore compared to footballers of today. Hell there was a twitter thread going around the other day about how Rio Ferdinand wouldn't make it in todays modern game, which of course we all know is a joke.
The fact remains is that Giggs made his debut at 17, had amazing technical and physical abilities a lot of players can only dream of having, he chalked up over 900 appearences for the club, won almost everything there is to win on a professional level, multiple times, and all this in a Manchester United side that remained pretty dominant for a good chunk of his time at the club. Was he lucky? No he was an important cog in that machine.