You're not supposed to roflstomp everything just because it's old content.
It used to be that iLvl inflation would, over time, make things easier. The "one hit one kill" legacy raid style came as a result of the first iLvl squish back in MoP: raids that were soloable became impossible to solo after the squish, people complained a lot on the forums, so Blizzard added the legacy overpower buff in response. This was never meant to be a solution to these problems, it was just meant to let stuff that was soloable before to remain soloable after the squish.
I think they've activated this effect for Legion raids now, which is pretty damn good since those used to be more soloable back in BfA with corruptions than throughout Systemlands despite 10 more levels and many iLvls.
Either way, the buff would ideally not be blanket applied to every legacy content. There's a lot of charm to being able to overcome legacy content on your own. And if you can't, you can get a few friends to come with you for a nice social experience.
It all becoming a joke should either happen naturally as we become just stupid strong, or as a peace offering after a botched squish.