To be pretty honest, I've done all the weapon upgrade questline until the relic+1, then stopped.
I've stopped because I'm casual player, mainly playing on evenings and I am not so much fine with things that I don't even know if I will succeed on doing them.
Please note I am really fine with things that require much effort to do them, it just means I will take more days to do them, but at least I know what the steps to do are, I will do them one at time until reach the goal.
The ATMA random drop part of this new weapon upgrade questline, have instead made me "meh", because it seems I can dedicate how many time I want on this, but the result will be totally random. The success of this quest does not depends the time I dedicate, nor by the skills I have to improve (learn the Titan HM fight, in primis), so I feel like I reached a dead end. It surely is not, but these are my feelings on this part of the weapon upgrade path was chosen.
I am sure the developers have already foresee behaviors like mine, and in fact have provided alternatives for that weapon. It means I (may) will try to get the alternate weapons, but I will keep the bittersweet feel to have left off something.