more effective during progression

In the "open world", for which I'll include dailies, Scenarios, open world PvP, dungeons (and maybe even LFR), similar levels of PvE gear and PvP gear would be equally effective. This would allow someone that's primarily into PvP and who gears up through PvP to still partake in vast swathes of the game content while not buy wow gold being effective at end game raiding, where it makes more sense for previous tiers of PvE gear to be more effective during progression.

Similarly, it makes a Mythic raider less effective in rated PvP activities, but still allows that person to casually partake in random BGs with friends or engage in world pvp activities, without having to completely regear to be effective on a casually basis?

I understand completely that at the opposite ends of the competitive spectrum of activities that it feels more intuitive for the gear gained by doing the respective activity to be more effective in the intended role; where I think it breaks down is the rest of the game in-between, which is pretty substantial.