I think most of them are OK to pretty good.
There is more difference between individual basses than between models.
The parts that you may want to change out would be the pots and tuners.
Most of them work OK and get the job done just fine, but in time they are more likely
to be the first parts to give you trouble.
Even then, I wouldn't rush out to change them before they wear, unless you
just want to spend money or change it just to say you did.
The pickups may be uneven from string to string.
Most are alright.
The most likely cause of people changing pickups is personal taste.
There were a few Protones that are even better than the Standards.
The only ones I would be sure to avoid are the Koreans with the plywood bodys.
Most of us don't like plywood, the necks are narrower at the heel and they used the very cheapest parts.
If you start off planning from the beginning to extensivly mod it, get a Chinese Affinity because they used
Alder for the bodys, rather than basswood or whatever was cheapest that day.