1) I don't think CA is adamant that the campaign should take 300 years. Maybe 300 turns. Anyway, there's not turn cap so it wouldn't matter because the game won't end. I don't even complete campaign objectives. I just play as I like. the reason they want it more fast paced than many fans want is because the average player wants those Imperial Segmentata clad legions that he can't have at the start.
2) Yeah, I'd like my generals to live longer as well.