Your views on hardcore honestly are irrelevant. But if someone can complete all the content in a week by spamming it non-stop it is poor game design. A mmo must be unbeatable by both hardcore and casuals, if it is not is simply must be considered seriously lacking in content.
We hardcore are upset because we feel with no limit, the game will never have enough valid content... there for always be a game where it forces us to quit for months at a time waiting on content. This is an issue in many games, while it is ok for casuals like those you described who play a online game for a few hours a week. For a gamer it is simply not enough.
The limit does not have to be a time cooldown, link it to the company related activities or something. Make it like you need X company current to buy a token which lets you enter the dungeon or something. This makes you focus, makes you do all the content added, makes you not spam 1 thing non-stop. You know tie the various game elements together, was one of the great things XI did.
In the current form I can guarantee you this will happen. Cap level players will spam the crap out of the dungeons. If the drop rates are decent people will rage the content is a joke like the NMs are. If the drop rates are not decent... it will piss off the casuals and the hardcores will get burnt out form spamming it and quit anyways...lose lose there.
The main issues in the game are balancing the limiting factors... leves are main source of leveling so limiting those is bad, dungeons are endgame not limiting those at all means you spent 3 months of work for potentially 1-2 week of content..... that is really really bad.
The solution is not to put cooldowns like leves, but to have some entree limiting factor like credits or a currency from doing other activities in game. That way while you can do them as much as you want, but eventually you have to do the rest of the game as well to continue to get access.
All reward and no work will lead to the game simply crashing and burning. SE has to imbue a feeling of true accomplishment into the game... or it simply stands no chance. Cheap thrills or unchallange material that simply rewards us for playing the game will not work.