That's not really true though. One of the things about 3.x that always really bugged me was how it coupled combat ability (which is represented by level) with someone's skill at a non-combat task.
It was indeed a mistake to tie those together
in every case. If, however, the Expert class had opened a "Master Craftsman" prestige class that removed the ranks/level tie but not had any BAB increase (or something like that), then that problem would have gone away.
Ultimately, though, I agree with you - while the NPC classes were extremely useful in some instances, trying to model the entire world with them was rather problematic, to say the least!
(as I first realized this in Star Wars d20 when I tried converting an old WEG Star Wars module where newbie PCs helped rescue the designer of the original Star Destroyer).
Ah, now this is a bad example, because even having a single "designer of the original Star Destroyer" is sheerest madness. Something like that would have been put together by a massive team of architects and designers, using the best possible software tools (and building on prior art). With all the sub-designers applying +2 bonuses from Aid Another, that project lead might well have been only 5th level (albeit with maxed ranks, the appropriate skill focus, and a high attribute bonus).
But more than that, crafting a Star Destroyer, although a task of massive size and scope, probably isn't inherently all that difficult (in the context of SW-galaxy technology). It would be comparable to designing a new class of naval vessel in our own world - sure, the skills involved are pretty impressive, and it's a lot of
work, but none of the million-and-one substeps are inherently superhuman in difficulty.
Let's use your example of a blacksmith who can forge mithril, who you insist is made using the expert NPC class and with several levels in it. Compare that character to a 1st level Warrior, who is a professional at fighting. The expert, if they've got four or five levels, is harder to kill and more likely to hit a target,
Yep, I agree with this. You
can build the Expert so as to negate this oddity (by assigning minimum hit points, or whatever), but that's certainly a dodge around a mistake in the system. As you note, tying BAB and max ranks to level in this way (and then trying to model the whole world like that) was a mistake.
and given they've presumably got wealth appropriate to their level is able to equip themselves adequately.
I do, however, have to take issue with this. Yes, the smith will have greater wealth, but if he's actually built as a smith then that would take the form of his home and his forge, masterwork tools, and the like. Equipping the Expert for war and then claiming
that as an inherent weakness in the system is a bit of a stretch, IMO. (Well, in the general case. Of course, since we're talking about a blacksmith, it would be entirely reasonable for him to have a masterwork morningstar and masterwork chain shirt lying around. He shouldn't be using anything better than that, though - he's not proficient with martial weapons or medium armour.)
The blacksmith is better at fighting than the person who has that as their profession, not because they're supposed to be good at fighting but because they have to be to have the skill levels they require to be able to work mithril.
Yep. The Expert class is of some use for those occasional NPCs who spend significant time travelling with PCs, or who are themselves somehow epic (it's not unreasonable that a legendary dwarven blacksmith would have some significant combat abilities, for example), but it's not really a good idea to try to use them as the basis for modelling an entire world.