The "Light" system is effectively the same "level" system that Bungie had for Yr1 that we all hated and criticized with one small twist. With the old system people hated that your level was initially based on progression, but was ultimately dependant on gear from one source, making any variety non existent (plus some low tier/level players also didn't like having to raid boost their light level, but without a high light level, they basically can't raid; thx to some LFG posters). New system is 99% the same, with the small twist that after you grind enough, you might get enough garbage to infuse other legendary items up to the same level as the raid gear letting you have some variety. In practice this is flawed as, why the hell would anyone scrap my highest their gear that gives me perks for highest tier activities, for what is usually very basic armour.