Might not get this unless it really sounds good and they really do have a good narrative arc involving the three characters.
After AC2 I didn't want more of Ezio, his story was done. Desmond was the linking character and we should have got AC3, a new setting, a new timeframe and a new historic assassin.
Instead we got a cash in expansion that added multiplayer and further refined the gameplay while barely advancing the narrative arc and featuring a now fairly dull Ezio whose story felt played out.
At this point AC to me feels like a great example of the challenge of sticking to a planned narrative and comercial interests. After AC2 sold as well as AC and everyone gushed about Ezio and the period it's just felt like Ubi went "great, more of that, stretch out the plot anyway you want and add MP".
I could be wrong and the narrative was always intended to keep Altair and Ezio involved, but a lot of the available background interviews from earlier in the franchise strongly imply each title was to feature a new period/assassin and built to a clear resolution involving Desmond in his "present day" timeframe. I really feel it's likly Ubi cynically changed course purely for commercial reasons and I've always felt suspicious that the change seemed to align to the departuare of one of the origianl key design leads.
Try to be reasonable... its easier than you think...
