Idk about rant, I see a lot of assuming though. You are assuming legendary will be able to be looted normally. Assuming you might get them as normal quest rewards,if T6 becomes the legendary tier, then it would make no sense (beyond finding parts of a legendary) that probably have random rolls and can't be used interchangeably (no using a shovel handle to make a pick etc.) to having crafting Q6 work, looting and questing should become the only ways to achieve that (yes "oh no looting is OP nerf nerf nerf!") but some poor unlucky soul out there may have stashed one in an out of the way location and never came back for it...
Lootability: depends on maybe the tier of the building (.01% in tier 1 buildings up to like 5% in tier 5 buildings, so location would contribute to finding them) outside containers might be loot locked to maybe a .5% chance, which isn't big, but still has a chance for some random garbage bag to have a useful legendary (maybe some survivor was rooting through it and dropped a Q6 hunting knife when he fled zombies)
Questing: would depend on difficulty have tier 1 have 0% (sorry no chance straight out of the gate) T2 have .01% up to T5 having maybe a 5% chance (since most T5 quests are in T5 buildings, that's 2+chances to get one {loot containers all have that small chance and then the quest itself [having Daring adventurer high gives the same 5% but multiple pulls from loot table]}
this above (rant? satirical phrasing?) is just my views
I was thinking more like a special treasure map that spawns a horde of specials, or a boss. Or a quest where you have multiple objectives from the trader. (retrieve special weapon part, then craft x item and y item in a workbench and chem station and return to the trader for a chance to see if he can revive the legendary item)..
Its all speculation though on both our parts. Who knows how it will end up when they are done. We sure dont.