With benefit of hindsight you can say all of them were flops. When Pogba was signed, we signed a promising CB who looked level above anyone we have, arguably best player from Bundesliga, best player from French league. We also had much younger Mata and very highly rated Martial who had brilliant season, Herrera who was rated as our best CM and even now he is rated as much better than Fred, McTominay. Then the magic touch of Jose to turn everything into shit.
When Bruno was signed, Rashford was injured. So we had James, AP, Mata, Lingard occupying 3 positions behind striker. Greenwood was barely a regular player at that time.
You can flip the question, when was your confidence of winning league higher, in 2016 summer when Jose was signed along with Zlatan, Mkhi, Pogba or in Jan 2020 when we 5th in the table after 2/3rd of the season, 14 points behind Leicester and level on points with teams like Wolves, Sheffield United with Ole as manager who had no track record of success at top leagues?
Ofcourse there is evidence of his impact, the position in the table and the teams we were competing in Jan 2020 compared to now. Bruno is also criticized like Pogba or any other player. His thread after every game is hard to read.
Yeah Pogba gets more criticism for some weird, maybe because people see him as a defensive liability when we have messed up the balance of the team.