The final mission in Conquest was quite the slaughterfest, lost half of my team and finished the boss on the last round I could possibly have survived, considering all my healers died. I'm quite happy I could complete the whole game with the additional restriction of not ever buying any weapons (other than healing staffs).
Effie was really amazing in my playthrough. At one point she surpassed even Xander in usefullness and she became almost indestructible. Including magic. On the other hand, my usual playstyle of using archers and magicians did not work out so well in Conquest. The level design asked for tanks a lot from my perspective, so Effie and Xander were incredibly important. I have trained three archers to level 20/20 and also two magicians to 20/20 (Nyx, Corrin's wife, and Leo of course) but the usual turnaround point where these units could survive off their own instead of being hidden behind other units never came in this game.
Now, on to Birthright. The first Birthright mission is supremely easy when compared to the first Conquest mission, so I'll wait and see if I'll be as happy with Birthright as I was with Conquest - which was truly amazing. Also, it took me 102 hours, being the first game I reach triple digits with since the GameCube days. If Birthright and Revelations are not considerably shorter / easier, Fates will end up being my most played game ever.
To conclude my comments on Conquest: I feel my valuation of the hardest missions in the game is a bit different than usual, my ranking goes:
22
endgame
25
I actually found 26 to be rather easy, at least if one ignores the fact that the boss was a lottery because it would have killed any of my units with a crit, none of my units could kill him in one attack and the one with the lowest probability of being crited, Xanders, still had a (I think) 8% chance of being crited. Luckily, nothing happened to me and I made it through that mission on my first go, which is unusual, considering my absurd play time. I really hate this randomisation stuff and cannot see the value of random events that can enforce a restart. Random cost me a lot of hours in the game, because in only very very few maps of the second half did I find a strategy that always had all my characters at an absolute 0% chance of dieing from crits (including the nasty crits oneself deals out in the enemy phase, opening up the character for more attacks than wanted) or failed attacks.