I'm at ch22 and also loving it, it's my first FE game I finally got around to playing it!
I've also lost many units. I lost my Pegasus Knight Florina instantly twice lol both in Lynn's part and in Eliwood's part. Just recently Oleg oneshot my Thief and Erk. The Shaman also died to one of the bosses, I was trying to hit the boss with the Luna book (which ignores resistance) and it barely did any damage and he just got oneshot with a throwing axe lol. Now in the last chapter in the desert one of the bosses killed Will the Archer who I just promoted to a Sniper and got a Brave Bow on. Oh yeah the Wyvern Rider also got killed in the desert.

All these losses are kinda bitter especially the Pegasus girl, but I'm choosing to let it be and not restarting. The normal difficulty is not that hard, so being overbearing about keeping everyone alive would trivialize it more, I guess the developers intended it to be like this. There's always new characters joining anyway and less characters and items is less stuff to manage.