My take on Samurai as a tank

[Shippuu]

DRK was fight club, or persona 4 if you prefer to face your true self. Later on you move to vigilanteism but that resolved with the realization that a DRK only going for a duty to protect is bad at what they're doing. Didn't play AST so can't speak there.

The second half of the DRK storyling (50-60) very much had you acting like a bodyguard more than anything. No different than the Ninja 50-60 quest where you were assisting someone to obtain a goal etc. In fact the DRK story is more of a bodyguard considering you're protecting someone who couldn't fight for themself. The NIN one is you pretty much just tagging along someone else's journey.

SAM Job's story will certainly be in question as it may focus more on being a Samurai not fully loyal to anyone due to the WoL being a Adventurer.

Then they have to cover 3 Story Arcs of SAM Job's storyline as 30 - 50 is Arc 1 (aka The Apprentice Arc), 50-60 is Arc 2 (aka Master Arc), and if things follow the same lvl 60 - 70 is Arc 3 (aka Grand Master Arc).

This assumes the new jobs will start at level 30 which could very well not be the case. There is a possibility of them starting at a higher level as well. I would prefer them to start at 30 again, but it's definitely possible they could start as high as 50 if the level cap is increased to 70.

I guess the one thing we need to address is the event we had pertaining to FF11 and the Samurai we helped, didn't she use like a Naginata? Would that perhaps be our clue to what SAM will really be?

There's nothing to really address. She's a character from FFXI in a crossover event, while she remains in Eorzea and it's possible we'll see her again, she will very likely have nothing to do with Samurai job quests if/when they add SAM.

People said all kinds of similar things about all kinds of NPCs, that Yugiri would train the Ninjas (She didn't.) That Merlwyb would train the gun class (She didn't). Even wild things like Raubhan training the Dark Knights (He didn't). The Job trainers are generally new NPC's so their stories are more self contained barring a few exceptions.
Adding Samurai and making them use Naginata (Already covered by some DRG weapons) would be a great disservice as in no Final Fantasy game besides FFXI have they used polearms. To add a job and not give them their iconic weapon is a ridiculus notion and highly unlikely to ever happen. While Katana are a type of sword, in Final Fantasy games they have always been their own classification of weapon.