One of the most difficult fights in FFXI 75 cap was "scripted" - Proto-Ultima in Limbus. You knew that Dissipation, a nasty ability was coming every 20% and you'd better have a BLM or RDM/DRK on point to stun it. You knew when someone was getting targeted by Citadel Buster and that you had about 30 seconds to GTFO (only element of randomnness was who got targeted. If they were a tank, they MIGHT live.)

And yet groups still struggled to clear this fight. We had an easier time with Omega, who was a lot more random, but whose abilities were a bit less totally-wipey.