She's just not very interesting or fun to play as compared to all the other characters. Players will like, split hair follicles to try justifying the usefulness of her so they don't have to admit Klei made a meh character. But just from a gameplay perspective, she's boring.
Like what does she do. She gets a free hit from Charlie, which changes nothing in the gameplay. She can make things faster, which makes things slightly faster. And she can make an alternate version of an existing item, which slightly changes how you use something already in the game which you seldom use anyways.
It's not even that she's not super powerful like most of the characters, which she isn't, but it's that her gimmicks aren't fun. Every other main character other then Wilson, even Wes, was designed to fundamentally change something about how players interact with the game. Which is what makes each character special and interesting. Winona doesn't do that though, all of her gimmicks are extremely passive and make little impact in the gameplay. Compared to all the other characters in the game, it's like Winona is a default normal Stormtrooper and every other character is an Overwatch hero. At least Wilson is iconic and his beard serves directly useful purposes.
Winona is the first new character ever in DST, and she didn't even get featured in The Forge trailer; what did Klei really have no enthusiasm to show off their brand new character in the brand new event they made which was the exact time when you would do that. And in The Forge itself, they couldn't even come up with a unique role for her to have. They just made her the generic, shapeless Jack-of-all-Trades character with a generic Jack-of-all-Trades tiny passive ability. It's like Klei has either run dry of ideas for new characters or they just don't actually like Winona.
They could at least make it so her tape repairs basic equipment; which is a thing people were hoping for from the very start and they still didn't do it. Makes no sense why they are just leaving her like this, at least nerfed Willow has some unique items and mechanics.