Every FF game with a job/class system has been this way. They all made use of cross classing to get the most out of the game. This isn't new. If that scares people, than maybe this isn't the game for them.
Cross classing itself isn't the issue I see. I think it's more that if you "need" to rank a class up to play the class you want then it's a problem (And saying they did it in XI doesn't change the fact that the system could be better in XIV I mean that's what were going for right a better game?).

The way I "think" it should work would be that if you want to play a tank job you level up your tank class. You can then tank but people will need to do things like wait 30 seconds/hold back on DPS. Every class you rank up after your initial tank class should ease the fights your doing. So if you rank up con suddenly you can heal your self for more enmity and DD can output more damage when they start attacking. If you rank up some other class that gives you the ability to gather a lot of hate instantly (Similar to a provoke but I can't think of a skill that does this) then your party would be able to start attacking from the beginning of the fight. etc. etc. making it easier for you to tank and/or the fight being completed faster

Instead of if you don't have 1,2 or even 3 other classes ranked up you just won't be able to be a tank.

Also I would like to say that just because something can be completed doesn't mean it's not broken (In this case I don't think it is broken though). Ex. People were able to beat pre-pre-(Is there another pre in here?)patch COP missions. Just because people were able to beat it doesn't mean it wasn't broken or isn't overpowered.

I'd say over all the update was far on the side of good but it wasn't to the point of perfection.