Need to address the Eureka in the room.

[Reynhart]

There's literally no reason for Eureka to be so punishing for solo players.

There's even less reason to purposefully play solo in Eureka. Anyone can queue then join a group inside that, most of the time, won't even care if you're actually targetting the same mobs as them, or simply doing your life elsewhere in the zone.
If you don't want to follow that setup, it would be the same as purposefuly do every content unsynced but at the same level of the dungeon, which is much more "punishin" than Eureka.

Yes, but I also noted that exp gains from chaining (Solo, or team) and FATEs was also garbage to the point that my time was better spent just doing Challenge Logs.

For solo chain, sure CL gives more, but each kill, in the highest zone available for your level, will still give a decent amount of Xp. As for team chaining, this is mathematically wrong, even before adressing that CL is only available once per week.

Which are in fact, more efficient to do in Anemos because you can easily find level 20 CL parties with which to blast through the killing of the mobs required.

Wrong again. Each zone provides easy spots to find mobs of two levels below you, that will take roughly the same time to kill, for much more Xp per kill.

FATEs are the ONLY way to get the worthwhile Crystals (As far as I'm aware. I have yet to receive one of the worthwhile crystals from chains. Even when farming for hours with max chain bonus in a party)

Only if you're of the appropriate level, so following the train to Pazuzu when you're level 5 is useless. But people still believed that it was a good method, and thus avoid chain parties, which made Xp slower for basically everyone.