I intend to make a full thread about that entire feature, but it'll take a few more days to confirm things.
Weapon fragments you get mostly for SELLING gacha SR and SSR weapons. Since we don't have skill point orbs yet, that's really retarded. But basically everything in this update is really retarded, so what can you do.
Additionally, for the new Lucent weapons you need lots of... a thing. Which has a retarded dropstyle. In short, this is what I posted yesterday in a Discord:
[11:16 PM] Slashley: So, in order to actually get drops from solo Battlegrounds, you really NEED to bring a full team of matching weapons...
Which probably means a full SR/R team...
11:19 PM] Slashley: I guess it's meant to teach you how Lucent weapons work.
But all it does is teach how trying to make a team of the same type of weapon SUCKS ASS.