By this logic, every job designed in FFXI is definite. I guess you're right, just like how FFXIV's DRK is the same as FFXI's DRK. Not to mention SAM was initially implemented to be a tank (and NIN to be DPS). They were designed so poorly, minus and minus became plus. Also, SE was on the brink of releasing SAM as a tank for HW. Everyone knows about the story that they chose DRK to be the tank for HW at the last moment. I would not call it a wild guess if they already had an idea for SAM as a tank.
I completely agree with your battle system change. However I look at it from a different angle. If they continue like this (1.0's cross class remnant), they limit the options for new jobs. They already had trouble with Ninja, hence Rogue is this weird class no jobs can get abilities from (jobs, not classes. Classes can, but I have yet to see people use classes in 4/8/24 man PvE). More trouble for HW. New jobs now don't even have a base class and start at 30. I would love to hear SE point of view on this matter.