EXP gains aren't well balanced in general. While leveling an alt job is a slog, you gain way too much from the MSQ.

I'd just reduce general EXP gains by about 20-30%, including MSQ rewards, and then increase the Armoury Bonus to counter this, maybe by +50%, to make leveling alt jobs easier.

You're expected to try out different jobs, and leveling is by no means a huge hurdle to overcome, but it could put off new players who end up disliking their first chosen job.