You compare it to the MMO argument, but this is a general thing from anything that has progression.
At any point in time of your choosing you can go back and rerun any story mission you want, the enemies still drop engrams, and you could use any of that gear if you wanted to. But you wont. Now why is that?
As for the content removal, yes the vendors now sell gear that dominates the original vendor gear in the base game, but VoG still drops VoG gear, and the strike playlist of the required level still drop their relative gear, same for Crota's End.
This is not new, this is not MMO, this is not RPG, this is progression. I doubt you still wear your baby cloths just as much as i doubt you care about lv3 white items.
TL:DR-- Current becomes old.
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That would make way too much sense