Is Winrate Really the Only Thing That Matters When Discussing Whether a Character Is Good Or Not?

Any time I try to have a discussion about the things I think are bad with Rocket, or why I don't think he's very good, I just get slapped in the face with a bunch of "yeah but he has one of the highest winrates so you're wrong and stupid".
I main Rocket and I got to Diamond with him.

"Rocket has slow heals and can't keep anyone alive through high damage or burst damage."
"Yeah but he has one of the highest winrates so..."

"Rocket can only do good damage if they are in his face, while other supports can do damage at much better ranges and much more consistently"
"Rocket has a really high winrate, you don't know what you're talking about"

Literally any time I try to have a discussion this is all I get.
Is it really the be-all-end-all of "proof" on whether a character is balanced/good/bad/etc?

I mean I don't think it is. Take Moira from Overwatch.
She's very very good at lower ranks. VERY good. She's a noobstomp character. Looking at Overbuff, she is consistently in the top 5 of both pickrate and winrate.
But she's bad at higher ranks, she's awful up there. People constantly talk about how annoying she is in lower rank, but the higher you go the more useless she becomes until she is almost never picked. Even the devs agree because they keep buffing her to be more usable at higher ranks, but it barely helps.

So what is it? Am I stupid and Rocket is the best support in the entire game and I need to shut up because winrate is proof that he's totally fine and never needs any changes?
Or can he still be mediocre and not very good even with a high winrate?

Edit: A lot of people are saying he's an off-healer, or better as a 3rd support. If that's what he's going to be then he needs to be able to do more than just heal. As he is, the Rocket player can't really take their finger off of right click for most of the match. I know from experience that doing that and trying to be aggressive and go in for kills will usually mean someone's death. This playstyle sucks. So he's an off-healer because his heals aren't good enough to be main healer, but because his heals aren't good enough he still needs to just spam heals all match and has almost no time to do anything else.
Meanwhile the supports that are main healers have time to weave in other things whenever they want. I still think Rocket should be designed to be played more like Mantis or Adam Warlock. I still don't think it's fitting for Rocket's character to just hang around and spam heals on everyone for 98% of the match when he's always portrayed as a character that's doing damage in every piece of media he's ever been in.