@2P51: If that is the case in your opinion then they why bother with stats at all?
You bother with stats because you're comparing capabilities to a desired outcome, which is only tangentially related to the PCs, their XP, and what they've spent it on.
If you go through all the trouble to make an opponent who happens to be an Engineer to be on par with the PC's Engineer, and you only use it for a combat encounter, then you've wasted a pile of time giving the NPC "Gearhead" and other Talents that are going to be irrelevant.
I would say that depends on your players. I have been in games where players were bored at the beginning because they kept getting knocked unconscious and were only really interested when they got to the higher levels and could really do a lot more.
Maybe they got knocked unconscious because the challenge wasn't scaled appropriately.
Yes, and not having a good way to compare (or at least an understanding of how to compare) an NPC to a PC can help alleviate this.