Now note that in addition to lower con the 18/2 also loses the capstone for less dps
So that monk splash looks like a gimp in comparison...of course the major advantage for that build is the evasion gain.
He is using the same bracers/armor/trinket slot as the pure, but he also has another slot burned on chattering/grim's and whatever slots he needs for wisdom (clearly the dex both are investing in though

) meh missed the abishi only being on one and not the other...air guard proc happens decently on the bracers so that is situationally a +1...so gear slots I think the abishi should be on both to make sense here bumping up the monk by 3 or on neither dropping the fighter by 3...the chattering needs to stay though as that is a no brainer piece of gear with the gear slot difference noted then.
24 dex is not insane by any means. It is 15 starting + 6 item + 3 Exceptional (tod ring + epic slot somewhere)...that is ignoring any tomes so yeah not insane at all...so really a 14 starting + 6 item + 1 exceptional + 3 tome which is really very reasonable.
Oh and another advantage to the pure fighter is they can throw on a shield to get even better AC without messing around with their gear setup. The other build could also, but they would need some major gear shifting to pull this off in a situational basis where it might matter.
So I would say as close as possible the monk splash has 3 more AC, but is running with another gear slot used for AC (at min).