The “mercenary contractor” politician has been a game changer. If one starts in imp., one misses this politician. And if one starts the game before imp., one cannot age up in DM for some odd reason. Though this has always been the case (in AoE III that is; in AoE II one could go up to imp. in a non-imperial DM start, even though it’s unusual), it never has been more disappointing. Before DE came out, pretty much only the Asian civs. suffered from it, missing their wonders. While a shame, it wasn’t too big of a deal, considering those buildings are very vulnerable to an infamous “cav. box” snipe (see Cav Box) and their bonuses aren’t therefore assured. But the “imperial mercenary” upgrade is “cav. box” safe and really important for mercenary-heavy civs. like the Germans and especially now Swedes. (To a lesser extent, if one considers the Age III mercenary contractor, some other civs. as well).
There is no reason whatsoever why going up to imp. is impossible in AoE III in a DM start. It’s imo long overdue this anomaly gets fixed.