I'd wait to find out how the light level affects damage output in TTK before writing them all off.
If damage intake is determined by your level and Light, and Light is an unweighed average of the Light on all your gear...we should be fine. Example.
You have a full set of (let's imagine) 400 Light gear and you're level 40. Please note I'm making this number up and don't know what the Light cap will be for top tier TTK stuff.
If you've got 400 Attack Primary, Secondary, Heavy, and a 400 Light Ghost, with 400 Defense Chest, Gauntlets, Legs and Class Item...and then your old 160 Defense Helm of St. 14.
Assuming an unweighed average across the light level of these 9 categories, your average, or Light Level, would go from 400 (with a full suite) to 373 if you rock an old Exotic stuck at 160 Defense. This is about 93.33% the hypothetical 400 cap.
Assuming activities aren't Skolas/Scrota style and have us play under leveled, rocking a single weapon or armor piece at Year 1 cap shouldn't have too significant an impact on damage taken/received. This, of course, relies on several assumptions I have no way of validating yet, namely:
- That Light is weighed equally across these 9 slots (if it were, Light Level in the Stream should have been 187 and not 186 though right?)
- That damage output/intake scales linearly with averaged Light Level
- That the 160 cap for year 1 won't be too far removed from whatever the new cap is (I chose 400 as a worst case scenario, I can't imagine it'd be that much higher)
Kind of hope this is the case, as it would mean that wearing an old Exotic piece would place you only a marginal disadvantage (as opposed to dropping a full level with the current system).