It's not marginal though, you look at someone like Ederson or Alisson and they are retaining possession with 15/20% more of their long passes than De Gea. They average 1.5 and 1 sweeping action outside the penalty area per 90 minutes despite playing in teams that keep possession considerably better than us, whereas De Gea averages 0.2 (yes, one action every five games) in a team that supposedly wants to play a high line - the worst in the league. Again you look at crosses, De Gea has dealt with 3% of crosses into the box this season, the worst in the league. The two aforementioned are at 8% and 9%. The differences aren't marginal, they're huge.
To bring this back around to Henderson, his numbers last season in terms of long passing were slightly better than this seasons De Gea numbers (only around 4% better so well short of Ederson/Alisson), but he dealt with 8.6% of crosses and averaged 1.1 sweeping actions outside the area which was why we were able to play higher up the pitch in front of him. So when people say Henderson may not be the answer long term but he's a better fit than De Gea for our defence, it's a view that is supported by the statistics as well as the basic evidence such as more clean sheets, much higher win % etc.
There's nothing "suddenly" about this, he's been a massive problem for years. The difference is people are finally, slowly, starting to see it.
