You make a number of valid points. I would like to just start with a small aside. You posting a link with an infographic describing a class you want to see implemented basically ensures it will never see the light of day. I wont go into detail here (this could be a book, and, sadly, probably is) but to summarize: US copyright law makes it a really fishy proposition to implement an idea unless you have a legally binding contract saying it is free to use, which, unfortunately, does not a forum sig make. I haven't looked at your link as I am a designer myself, not for this game in particular but for a number of other projects, and hope to work for SE some day. I am sure you are not the type of person to do this, but say they implement a class that functions very similarly to your Fencer and you decide that your idle musings constitute intellectual property. You could sue because you think you deserve a cut of the cake. If you did that, SE would have 2 options, either pull out of North America entirely (which means we miss out on the next FF and KH along with any hope of a Kingdom Hearts ride at DisneyWorld) or face your lawsuit and potentially lose all North American profits from the expansion your Fencer was featured in, which could easily snowball into all the money they had earmarked for other major projects like KH3 and FFXV.
Now, onto the meat of the issue.
In short, a perpetual model game with no mutability is a boring game. Market analysis indicates that even consumers of entertainment that like the original product eventually get bored. A useful analogy is as follows: say your favourite ice cream is Oreo chip. Every time you go out to eat you get Oreo chip, maybe even a second or third scoop. Now, imagine if you were somehow magically constrained in such a way that you could only gain sustenance from Oreo chip ice cream. I know my favourite food is lasagna with swiss, parmesan and sausage but by day 3 of lasagna I want a freaking cheeseburger. Same goes with entertainment. You would eventually get bored of the same version of Bard, just like everyone else. It really sucks when this change doesn't happen by your schedule (in this analogy, the parlor runs out of Oreo chip before you're finished), but that's okay, there's still lots of other flavors. Oreo chip will be back some day and it will be even better than you remember. but for now you should try something else.
I fell in love with Strawberry when my favourite ice cream shop stopped selling Oreo.
This sounds like an argument borne of EA and Activision. Yes, a lot of companies release shoddy, unpolished games and expect players to provide free feedback. SE, however, has no history of this behavior. Many issues (such as exploitable loopholes in a class's spell list) will never come to light at an in house testing division without literally millions of testing personnel. In house testing is good for mechanical testing; "does this cause a fatal exception?" "Are all the walls solid?" "Does this boss reset every time the White Mage casts Cure?" etc. Outside of those issues, its really kind of impossible to see how everything works until its in the hands of the masses.
I must remind you that SE is a firm couched deeply in the traditions of cinema and literature. Its a very real possibility that they believed this thing would never leave the ground if the players already knew what would happen. Yes, the belief that you can't even reveal the class list without ruining everything is a bit silly but we must all remember the pedigrees of the game designers whom are, ultimately, mistake prone humans. They could have done better in the lead up to this thing but all we can expect them to do is tweak their strategy from here on. The past (no matter how immediate) can't be changed and its useless to punish them so harshly for a small misstep.