So my main is an Arcanist...

[Themis]

I do hope SE will either fix this later on in the game or in the future not make the same mistake again :/.
I'd hate to play THF with STR instead of DEX which might be THF's main stat in the future but who knows lol.

It's not a mistake what they have done. What they've done is required you to make a choice. That's the design of it. The issue is that some players are min/maxers. But if that's a problem, then level an alt character and have 1 be SMN and 1 be SCH. When the 2nd job comes for all the other classes, you can level 1 set of Jobs on 1 character, and the other set on another.

Personally, I like that you can't be the best at everything. You can level up a variety of things, but to be the best or a master at something, that requires you to be more committed. Or, you can balance your skills and play each reasonably well but not being the best in either. Plus, gear and skill make up for any real loss in the stats, and for SMN and SCH, the INT can be far more beneficial for both whereas MND only really affects SCH.

If a merit point like system (from FFXI) comes in, I'd be quite content if it worked in a similar way. That, too, made you choose where you wanted to specialise. You did that by deciding what your main class was, and focusing on that one primarily.

[KraggyKor]

The issue is that some players are min/maxers.

Yeah, and usually it's the min/maxers that are telling players like the OP that they're gimp if they don't put all 30 into INT or MND as appropriate.

That said, +30 to either stat is not an insignificant percentage of a 50s' INT or MND so it's not easy to dismiss it; it's not like a case of, say, 0.1% which the min/maxers argue is huge when in fact it's entirely worthless, FFXI's +1 gear being a classic example of min/max hyperbole out of control.