Can't agree with the definition you are using,
It's like saying I can stab a guy on the street. Sure the police will throw me in prison and I will never see the sun again, but I can stab a guy on the street. Right?
Specialization != upgrade. Upgrade means you get more powerful as a whole - like when you level up. While specialization means you lose flexibility for strength in a specific area.
Specialization is a trade-off and in-game I think it's meant to be given that they limit your Cross-Action slots and the abilities that fill them. Jobs aren't suppose to be more powerful that Classes, in general. The fact that end-game gear is wearable by an ACN as well as the ability to even queue for CT as an ACN, at least hints to Classes being usable end-game. But where they failed is the implementation, e.g. +stats to Jobs, Job specific gear.
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I know some don't like me criticizing their favourite game - seriously it's a good game; but that doesn't mean I don't have complaints.
To quote FFXIV own producer/director,