What exactly is ranked globally vs individual server?

I know Arena is server-based. What about Legends Challenger/champion? My understanding is it's global, but if that's the case how in the world is it fair for servers that started earlier to compete with newer servers?

What about treasure scramble? Or Temporal Rifts leaderboards? And Wall of Legends?

Also, infact, how do the leaderboards for the three Hellscape modes work (TR, CR, NC)? Sometimes it's separated by "floors", sometimes "regions", sometimes it's just completely ambiguous. It's honestly hard to tell who I'm competing against.

What about for events like this Battle of Bloods thing? I'm at the top of my server, but it still doesn't register me on the "fortune chest" for my guild, so I'm guessing all event leaderboards are global?

On that note, are guilds completely global? Like, if the very first server had a guild the was recruiting, I could theoretically find/join it?