I think Lingard's combination of attacking attributes (good movement off the ball, keeps it simple with is passing, decent finishing) would look a lot better in a team with stronger attacking options elsewhere. I think in a team with strong primary threats he'll provide a lot of work off the ball, pop up to finish off chances and not step out of his lane. The problem to me is the current team is basically the opposite of that (we have a decided lack of primary threats) and consequently he doesn't contribute much at all. We desperately need an outlet in that spot which is why we look much better with Rashford or Martial in that spot (they're also better players than him overall, but fit is part of it). Still think he's a perfectly valuable squad man and should continue to contribute even as the team improves as long as the fit is right, but in the current team playing him ahead of Rash and Tony really hurts us.
To be fair, only Lewa walked for free. Bayern paid 80 mil for Gotze and ,Hummels. It was a good money just a year or two ago.