Literally no one is doing the last 3 you suggested which is dumb as shit and the first is already in place
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I just state options to have a sensible system. My main focus is legendary on legendary infusion costing 1 core. Also, people just getting up with power surge bounties and other similar stuff may find something other than legendary to infuse into their old guns and armor. I for one, leveled up all the way a titan to 700. Then I went to my warlock and got all white gear to powerlevel her for cheap up to 675 ish.