Its an error to have removed abilty to train thrall to level 20 with the event of the siege

That’s exactly my belief. I also think saving and hiring thralls as an option goes in that direction. Thralls would overrun us in a heartbeat. We don’t have a structure powerful enough to hold an army of slaves. It’s a good move from funcom.
I would also lower the stats of thralls coming from the wheel vs saved (highest) and hired thralls. These would be the backbone of our base. The wheels would produce cannon fodder, meat for the purge grinder.