Vantage was strong for a very long time, but for some reason the general sentiment was that she isn’t, and a lot of people weren’t even trying to see what you can do with her. When I’ve decided to main her in season 20, it took me about a month to go from “I’m not sure it was a good idea” to “Oh, I get it now”. After that I had quite a few cases when my random teammates were making fun of me on character selection screen only to stop joking about halfway through the match. But of course, my impact is limited, you need top players to play a character and discover their full potential to change community’s mind.
I think this overpowering of Vantage may be done intentionally to make pro players pick her (and it works, at least in ALGS APAC North). Something like that was happening with Alter – she wasn’t weak from the start, but she wasn’t seen as such. Then she got massive buffs, became a must play, then she got a lot of nerfs which in some areas made her weaker than she was initially, but because so many people have already realized what she allows you to do, she is still considered as a very strong character.