While I can see you like the individuality you seem to have in this system the reality is end game shells will choose the dsired set of skills, that see as most useful and then everyone will be a,b,c,.
I like customization. Most people do. I think most people approach XIV with the mentality of other MMO (including and especially XI + WoW) where what you're saying is true.
I'm not saying you're wrong but I will say you aren't right yet. There's no clear way to tell what the original end-game intent was going to be (and now we may never know considering there is a new direction the game will head into sooner or later).
You're suggesting that an end-game fight will require a certain desired set of skills - but the beauty (as I see it) is that any job can perform that skill and then later on (perhaps a different fight) set up an entirely new series of abilities to optimize that fight.
Take what's in the game now - these silly handful of NM - and then say LSs with serious intent prioritize a well equipped Pugilist who can break Dodore's Tail (or whatever). Well, anyone can get that ability and use it on any job (though it would take work, and playing PUG to near the cap) but if you don't want to play PUG and you do want to be included in this activity (and assuming your LS requires it for you to get invited - which would be jerky but not unbelievable) you could do so.
Now imagine it's PUG only. Well, no more Archers invited to the party.
That's what makes the system great! You build your own class fundamentally. As long as SE continues to make 90+% of the abilities unrestricted - and continues to balance incapacitation throughout various jobs - and continues to build "end-game" content that is inclusive (so that any job is welcome barring they aren't completely ridiculous - like Glad with THM skills I described which is great for solo but silly for endgame) I don't really see your idea being much of an issue.
I dunno. I think this time around I may try to start my own end-game LS where my focus is having a good time and not the rampant elitist min/maxing shenanigans I see all over the MMO genre. You're -probably- right that no matter what I hope the future of XIV turns out to be there will always be (successful) groups running around with "perfect" builds being dictated to members.