I think the truth about Anderson lies somewhere in the middle of all this.
I think he's a good receiver already, with the potential to be a very good receiver, but probably not a future star (he's already 26, and in any case the Jets wouldn't be shopping a future superstar when they're trying to develop a 22-year-old franchise QB). That said, the Eagles don't need a Randy Moss - they just need an average fundamental WR who's also a blazer, because when your passing game lacks any vertical element at all, you become absurdly easy to game-plan against. Anderson will make Alshon and Ertz more productive just by stepping onto the field with them.
I think Manny Sanders is a better fundamental WR than Anderson, but I would take Robby on the 2019 Eagles 100 times out of 100 over him. Would I go the 3+4 price the Niners paid? Maybe. Anderson's up for a new contract, so even if he balls out and the Birds can't afford to keep him, they'd likely get the 3 back in 2021 anyway. (That's the exact calculus Howie had in mind when he traded for Tate, so don't think it wouldn't be a consideration here.)