Can someone explain to me the Atma quest/chain?

[AiChyan]

after reading all of these, I think I'd rather quit playing FFXIV.

You don't absolutely have to pursue this quest line though, you still have the sol weapons & high allagan weapons. I opted to stop at animus as novus requires too much work and I'm not doing anything in game that requires a very high ilvl weapon anyway.

[Aaramis]

You don't absolutely have to pursue this quest line though, you still have the sol weapons & high allagan weapons. I opted to stop at animus as novus requires too much work and I'm not doing anything in game that requires a very high ilvl weapon anyway.

Yep, exactly. If you're casual (like myself), your Zenith is enough to do 90% of the stuff ingame.
If you're a bit more into raiding, then Coil will net you either an unidentified tomestone (turn in for weathered weaponry) or your high allagan weapon. You can also go with the primals route and take out EX primals for the wave and thunder weapons, some of which are on farm mode now.

Up to you
I personally don't have any interest in the Zenith weapons line, as it's just a massive boring grind. I'd rather try my luck at primals or Coil (if I have time), but to each their own.