Also: An egalitarian culture, such as Przeworsk I (the one before the new upper class) was, and such as Scandinavia before the recent immigration wave, has very strong social rules in place to ensure that such a class does not arise from within.
http://en.wikipedia.org/wiki/Jante_law
http://en.wikipedia.org/wiki/Lagom
http://en.wikipedia.org/wiki/Tall_poppy_syndrome
A new prestigious upper class in such a culture can arise only as a result of violence from the outside. An invasion.
Thus we have one more problem.
****GK: These rules don't always work. In any case they don't prevent what we might call "democratic lordship" i.e. people ruling other people with their consent (at first). And in any event early Przeworsk was the result of an invasion (Jastorfers vs. Lusatians). There is no real impediment to the internal rise of lordships. Which of course does not deny that many such are also external invaders (maybe even from the next village (:=)))****