If what Betelgeuzah says is correct: Classes are tuned more for solo play, while Jobs are for party play. Correct?
Yes.

In order for one to be viable for serious group content, new players & old players would need to unlock and relevel a new class. At that point, isn't it just a roundabout way of doing a character wipe?
The levels are shared. Each class has a corresponding job. All you need to do is unlock the job for the class, and do the quests for job specific gear and abilities. If you want to solo/lowman, you play as a class. If you want to engage in group content, you switch to job.

The archetypes don't change, but they can overlap.