The Relic Weapon
It's an absolutely boring chore to upgrade a Relic in Pagos, chaining in XIV is not something I find fun at all. After one chain #30 I'm done, because when I look at the bar after one chain #30 it's hardly even moved. If there's a better way to grind light, then you'd best tell us. No one is going to care to even bother to find out what silly system you had to get above a "Feeble" light, even though "Feeble" amounts vary greatly, just another thing to confuse players. Pagos is already obsolete in it's rewards, there's no need to withhold how you wanted us to do this. The Stormblood relic so far has been the most boring Relic to upgrade.
The FFXI Items
They are way too damn rare. The Hakutaku eyes come from the bunny fates that people now rarely bother with due to either no experience reward or no light reward. And on top of that you'll likely only get Gil and Materia V/VI from those bunny chests.
The Cassie Earring comes from the NM Cassie that no one ever does anymore, very rarely will you see people bother with it due to the feeling of it being a waste of time, and it's true. The Cassie NM is way too rare of a spawn, or we are missing something, which again, you'd best tells us because no one cares to test it further due to Pyros coming out soon.
Arthro is the only NM that drops a FFXI item that I've seen worked on with regularity. However, I've never once seen a Speed Belt drop, or been in a party when someone said they've got a drop. I haven't even seen someone shout they got a belt lol. It's way too rare of a drop. This is not a good idea to have FFXI nostalgia items so rare when you create content that is going to be dead in a matter of months and therefore no one will ever get those items again due to no one wanting or needing to do it.
Possible Relic Solutions
Have light amounts increase every 3 mobs we chain, from "Feeble" on the 3rd to "Brilliant/Newborn Star" on the 30th. Perhaps varying depending on the level of the mobs you kill. So if you chain Lv35 mobs you won't get as high a light tier bonus as chaining Lv40 mobs.
Possible FFXI Item Solutions
This mainly comes down to simply increasing the drop rate of certain items. However, the Cold-warped Lockboxes should be obtainable from all mobs that are at least 38+, this simple change would make it way more desirable for groups to deal with the Ameretats to spawn Cassie. And on the topic of Cassie, simply increasing the rate at which she spawns would also encourage people to bother with her. Also as I mentioned above about the solution to change how light is accumulated. This might also encourage people to deal with Cassie more often if they can get a decent amount of light from chaining high level mobs.
Currently the bunny FATEs scale with the amount of people within the instance. I've completed both these FATEs solo on PLD in about 5 minutes when I was the only one in the instance. But when there's a lot of people in the instance it becomes quite the slog to attempt this solo and even with a party of 8. These FATEs should have light and exp amounts that scale with it's current difficulty. Albeit smaller amounts due to them being up constantly. This would encourage people to even think about doing these Bunny FATEs. As for the chest rewards, I've never once seen a gold. This need to be increased dramatically if you want people to care about doing these FATE again in future.
I have nothing to say on Arthro's Speed Belt aside from the same I'd say for all these items, increase the drop rates. FFXIVs content is designed in a way that after 4~6 months it's pushed to the side for something new. Therefore you cannot have super rare items within Eureka that people can reliably get like they did in Anemos, which had decent drop rates for these FFXI items.
During development focus on what's fun and not how long you can make players do a thing. Currently Eureka isn't that fun after you hit the Level cap. Thanks for reading!