I was 75 in Dragoon, Dark Knight, White Mage, Red Mage, Ninja, & Dancer. Actually, FFXI had no sort of class restriction system. Whether it was Kirin, Byakko, Bahamut V2, the kings, the Sea Jailers, Salvage, Einherjar, Limbus, Omega/Ultima, or what have you - the problem was more so that people were too damn lazy to gear up for their classes. Granted, I didn't actually get into or near endgame until after the 2hd update for my DRG & DRK, I did take a break from leveling my DRG when ToAU came out to level RDM & WHM despite the fact I had been 55 when ToAU came out and could've just leached on Colibri-based parties. Why? I knew if I continued, I wouldn't have been able to effectively gear myself. I had a lot of high-level friends, including a Gungnir owner & a Kikoku owner by that time. Being that I had practically singlehandedly built the single-largest DRG-only shell to ever grace Vana'diel (and I was only an officer of this linkshell, mind you), I found nearly every single DRG on Fairy and talked to others on other servers, I had come to realize that even though I was always good at outparsing others whether it was against crabs, ants, spiders, or what-have-you, it was obvious I needed to find a way to get better gear. (Interesting facts: I later left that linkshell, after being berated for choosing to level other classes to 75 first, those berating me for it later quit to level Summoner just because of the Dragoon-Emote update, and almost everyone dropped the linkshell based on my choice despite that I left as quietly as I did. When I finally did get DRG to 75, only a few others actually had better gear than me, while those that berated me if they even had DRG at 75 still had shitty gear.) So the real problem was and is that all the people that whined at least beyond the 2hd update (not before the 2hd update, since yeah, it was just stupid albeit Penta Thrust being changed was also stupid), while they may claim one thing or another their only real problem was refusing to gear up. (Oh and another problem with classes like Dragoon? They didn't exactly get Haubergeon-esque gear until ToAU.) Now to the content of your post: I don't mean just some sort of combo system, I mean enemies that are strong against one type but weak against another. Like how crabs should be strong against piercing & weak against slashing, while flyers should be weak against piercing, water elementals should be weak against thunder, strong against fire. There's no excuse not to have a type-weakness for enemy monsters, and yes I absolutely do mean having it so a class is ineffective at some events while effective at others.