FFXIV 1.0 & FFXI (11 years old!) both seemed to suffer from this netcode/structural issue - FFXIV ARR seems to be no different in regards to latency Client -> Server relationship. Since someone has already figured out how to dupe the checks (teleport hacking) going on between the Client -> Server I wonder why they don't move the priority to client side data a.k.a make the server back check your position against the recorded position of the monster without trying to actively reconcile position data server-side.
How this works:
Sever's apparent current method for checking position; Note this is active and relies on packets being sent to the server successfully*
Dhex - Space #1 @ 00:00:000
Dhex - Space #2 @ 00:00:300
Titan AOE Casting Appears - Space #2 @ 00:00:400
Dhex - Dodge - moves back to Space #1 @00:00:400
Titan AOE Animation @ 00:00:500
Dhex - Damage Calculated @ 00:00:550
Dhex - Position updated - Space #1 @ 00:00:600
vs.
Back checking Client position data via time stamp;
Dhex - Space #1 @ 00:00:000
Dhex - Space #2 @ 00:00:300
Titan AOE Casting Appears - Space #2 @ 00:00:400
Dhex - Dodge - moves back to Space #1 @00:00:400
Titan AOE Animation @ 00:00:500
Server check Client side data back log: Dhex in Space #1 @ :400
No damage calculated/applied to Dhex @ 00:00:550
How teleport hacking works:
Currently you'd need to inject packets with "false" position data for the server to read - by giving the server false information about your current position it makes it so that when the server next updates it will position you where it "thinks" you should be - rather than where you really ought to be.
Client side positional data can be found and modified but that's a problem for developers to work around if they go that route...