Something is definitely up with Magnar. Three games and in all three the AI Magnar explodes to a massive lead and kills everybody. I believe it is because of the slaves, it allows him to spam pioneers faster than everybody which snowballs into a big lead. I actually held my own against him this time for awhile using superior units, but the other AIs get smushed. Definitely needs to be looked at in view. Tomorrow I'm going to try a game as Magnar and see how abusive it is.
Which leads to the side issue of pioneer spam, on my 3rd game I clued in that you need to make a lot of pioneers very quickly and grab stuff. The problem is that it seems like pioneer spam is the only viable opening strategy. I'm not sure what can be done to address it, but it would be a shame if that proved to be the only opening strategy in the final product.
My suggestions:
1 - Place some kind of limit on pioneers.
a. Consume population or something
b. Cooldown timer on building them, say 1 per 30 seasons per faction.
c. A "pioneer" resource which all factions generate at 0.1 per turn and it takes 3-5 pioneers to produce a pioneer unit. In this way, a faction could accumulate "pioneer" resources and make a whole bunch rapidly or create a steady stream every 30-50 turns.