If Strome was replacing Hayes' offensive production, he'd have to produce for both himself and Hayes.
Just because he's produced the same raw numbers as Hayes has with WPG doesn't automatically mean he's replaced Hayes' production. To consider Strome having "replaced" Hayes' production, he would have had to have 20+ pts.
If we got Strome at the TDL and he was producing this much and in the same role, than yes, you could say that he replaced Hayes' production. But Strome was on the roster way before. So to say he replaced the production would mean you're now binning Strome into Hayes' slot, and someone else now needs to "replace" Strome's production, and so on and so forth. Of which, that hasn't happened.
This isn't rocket science.