*AFAIK cascading alliances were implemented because some players annoyingly complained that they wanted to include "their new-acquired" ally after the war has started, so they made that available, but doing so, they didn't want to handicap player too much so they made that possibility for AI also, and this is where you gett those cascades.
*White peacing
You can always just ignore them. AI doesn't get the ability to know, if player "would accept the peace offer" or not, and it's not even a big deal, it's not like it spams your screen, just ignore it, focus on war and try to win it
*Warscore
If in your situation, you got 40 warscore and couldn't get calais, even though you obliterated their armies, then it's something wrong with calculation of war-exhaustion, not warscore.
Let me put it this way:
1.)If an enemy has perfectly intact army and you have an almighty 90% warscore AI shouldn't even consider making anything worse for itself than a white-peace.
2.)If an enemy has an obliterated army, no manpower left and you have 10% warscore, then my son, you should gain wargoals, that take up 10% or even more sometimes.
And if it doesn't work that way, something is wrong, but definitely not with the warscores.