The way they chose to implement it, with learning spells from monsters and Primals, is really innovative and unique.

But I don't think we needed 49 of them at launch with more on the way.

Because there's going to be a set of spells that everyone recommends you have and everything else is just filler or fluff.

The reasoning they gave at the dev panel was rather weak -- "Oh you don't have spell X? Booted from the party" is no different than "Oh you don't have your paladin job stone? Booted from the party."

A blue mage who has taken the time (and had the patience) to get all the spells would be as welcomed in a party as a player who took the time to get their final Eureka weapon (and assuming they know how to play their job and do mechanics). That player took the time and effort to work toward a goal. Now the dev team is saying "Good for you, but you can't use those abilities in raid."

Then why have them at all???

A crafter who doesn't level up ALL crafting classes isn't barred from crafting things. They need all crafting classes to make end-game things easier, without a doubt, but they aren't completely shut out from it. If I'm an armorer and I want to craft an armoire, I know I'll need to level up carpenter. Not a big deal. Can I craft an armoire with fewer skills? Conceivably. Would I have an easier time if I leveled up all other crafting classes? Absolutely.

TL;DR: If you put in the time and dedication toward working on a goal, you should have something to show for your efforts that can be used in group settings.