Black Mage - the solution for everything?

[Nabiri]

...would be better if they add monsters specialized against these jobs, just like Colibries were anti-blm on xi, reflecting their magic...

I don't think it would be a good idea to make content that certain jobs couldn't participate in. If a person wants to have only BLM leveled for some reason, they'd end up getting left out. I believe a solution needs to be found but I wouldn't like people excluded.

...or monsters with high defense against certain weapons like arrows, that way there dont be always an unstopable job.

Something like this sounds better to me.. but they'd have to be careful not to make the job useless. If you weaken it too much people just won't bring the job. Making jobs balanced is easier said than done though. :\
I'm sure SE will think of something.