its definetelly a good thing to keep old content somewhat useful. they way they do it in Legion is ... not... useful. its fukin crap shit.
what i never will get is this: since WoD they have auto generated loot lists. they could scale gear ilvl of drop gear by 1 knob. why they implement fukin RNG stuff when they could just scale old content a little bit up to fill gaps in gear of new content ?
i.e. a while (maybe 3-4 weeks) after new content (nighthold, at the moment) is out, scale old heroic EN gear up to same or 5 ilvls above NH nhc gear. this could also lead to a world where some nhc only guilds do a little bit heroic stuff with a little bit outgearing. full hc guilds will not go back to EN that much. but for some specific slots to fill up and for something todo after id is done, it would be perfect. same goes for XR mythic content. some hc only guilds would love to play EN a little bit in mythic, after its XR, but they never do, bc gear is shit, compared with actual content.
i dont get why blizzard didnt tried this way, instead that horrible RNG nonsense.