The complexity is not comparable with Vashji.
You might compare it with Kael Phase 3&4 in terms of complexity, although this comparison is not good as Kael P3 is about DPS and 3&4 are about using the looted legendary weapons correct, all other things are rather simple in that fight.
Kalecegos is not a dps race, it is more a fight about surviving and comunicating.
If you are interested in it read on the boss tactics here.
The whole things gets complicated since you have to make sure that during the whole fight there must be a tank + two healers in every realm.
Furthermore everyone has to enter the deamon realm every 60-80 seconds. If he does not manage that, he gets killed by the arcane debuff (a 8 stack debuff ticks for 4.5k damage, at 10 stacks its 5.5k and so on).
You stay in the deamon realm for 60 seconds. You cannot go back early, and you cannot stay longer. Once back into the dragon realm you can not reenter the deamon realm for 60 seconds.
Once a player gets ported, a portal opens on his position which allows transition into the deamon realm (but you can't stand next to each other since everyone in range to the ported person (less than 5 yards away) gets 6k arcane damage which is further increased by your arcane damage debuff, thus you will get hit by ~6-10k damage)).
Once the portal is there you can go through it one by one (after one player is ported you have to wait 1-2 seconds for the next player to go through). You can get 5-6 players ported per portal.
The longer the fight goes, the more curses are flowing around. The curse ticks for low damage at start and doubles damage every 5 seconds. After 15 seconds it must be decursed or the player will likely die from 1k-3k damage ticks every second. If decursed, the curse does not go away, but hops to another player (and restarts there ticking for low damage again). At the end of the fight 4-5 decursers are decursing people nearly 100% of their time while 8-9 healers are trying to keep the whole raid alive.
All in all very interesting and demanding. But if 1-2 players get the port roation mixed up you loose. If more than 1-2 players die you'll likely wipe. If a course ticks for more than 15seconds the player has a good chance to die. If you are longer than 80 seconds in the dragon realm (e.g. you missed your portal), you will die.
If a healer does not make it through a portal, people in the deamon realm will die.
While Kael is a really demanding encounter it is a lot more forgiving. Everyone can loot the legendary weapons and everyone can buff/debuff people. If someone cannot manage to apply the dagger to mind controlled people, assign other players to it. Thus you have some leeway in that encounter.
Kalecgos in his current version requires a perfect execution of your tactic or you won't beat him. If a single group messes with the portals, or one player messes up you can not recover.
On the good side. It is a really entertaining and demanding fight and I hope once we have a bit more coordination and practice we will down him, and that will feel really great :-)
I only hope we make it during the next raid days before the boss gets nerfed.