Morale is definitely important. But on the other hand discipline can also influence the war effort in a major way. It's tough to fight the Ottomans at equal tech for example as Muscovy. Ottomans had about equal manpower to me, I had actually less Muscovite soldiers, but my vassals boosted it all to equal number of troops (theoretically). Ottomans dowed my ally Georgia thus came the war.
What can happen with enough discipline bonuses, is that you shatter enemy stacks in very fast time, it is impossible to merge stacks during combat, so this can lead to real meatgrinder type battles. Your own manpower reserves vs the enemy manpower becomes the true arbiter of victory. Can you win even if you have negative K/D ratio (sometimes it is heavily negative, with the 6 shock 6 fire godkings of the enemy)? Do you have enough fresh stacks to reinforce important battles?
I did notice that I had a really tough time in battles, even when defending where I had advantage 2:1. Ottomans maybe had small morale boost of some kind (from religious bonuses or advisor). Sometimes ottomans just voluntarily retreated which was annyoing (just before my reinforcing stack could arrive into defensive battle LOL)
On the other hand, the Ottos did have the much feared god generals also, together with their discipline boost from unique ideas. There was one particular 6 shock 6 fire general, ouch that was nasty. I have the save on my other computer, but the war didn't go terribly well sadly. Ottomans simply have too much manpower compared to my mp. There's no way I can easily fight them off, even though I had ton of gold before the war. (cant recruit enough mercenaries, to be at 1:1 odds with soldiers). And my mil tradition kind of sucks also, can't get good generals because coalitions kind of forced me to be peaceful for a while.
Warscore is tilting to ottoman favor also because I had a ton of vassals that I should have already annexed like Ukraine. It just sucks that you cant scorch your vassal territory, the Ottomans would have died to all that attrition If I could have done it properly. On the other hand, scorch earth would only have made my problem worse, spending 50 milpoints per scorch one time. It would allow Ottos to outtech me during the war.
I saved ton of money by not building too much stuff, I had really bad luck with multiple regencies and shitty kings, I was just expanding my vassals and colonizing. But I did just get overseas Asian CB from expansion tree, and just started the quantity idea as my first military idea, I went expansion religious quantity.
However lately I've been thinking about the Russian situation with Ottoman wars. What would be the best strategy for defensive war agaisnt them? It's not always possible to avoid war, sometimes they just dow you. (or your vassal/ally)
I was thinking about building a series of forts on the southern fronts of Russia. Strongest forts in the frontline borders definitely. This denies the enemy, the possibility of easy and quick carpet sieging the frontlines, with protecting stacks nearby. The bigger the fort, the bigger sieging stack it requires, which leads to more attrition. It will require more artillery regiments to siege. Siege will also last longer time, especially with a defense advisor.
More forts would be built in the southern climates, so that they must siege with bigger stacks, and face more attrition, sieges last longer. In the cold winter areas of Russia, extra forts are not needed, as the weather will do it's work on the Ottoman stacks.
Possibly the defense tree would be helpful in this kind of war, even longer lasting fortifications and doublle attrition from simply normal sieging (from 1% to 2%). And the morale bonus and less attrition suffered to your own side would allow nice counter attacks against weakened Ottoman stacks, possibly. But later on it would still require some kind of discipline boosting ability I think.