Jon's progression of Marks is so deeply devastating, because the further along he goes, the more Marks he gets from trying to save people.
His first 4 Marks (Web, Eye, Corruption, and Spiral) were things that were done to him. He didn't seek them out. Mr Spider was in the pile of books his grandma gave him. he had no way of knowing The Magnus Institute was haunted. Jane Prentiss hunted him down, and so did Michael.
the next 2 were brought about by his own curiosity. he knew the risks of accosting Jude and Mike, but he went willingly. his desire to seek out knowledge got him Marked by the Desolation and the Vast.
Elias sent Daisy to Hunt Jon, so that would make it the 5th Mark that Jon had no agency in, and the 7th Mark total.
then comes the Unknowing. in an attempt to save the world, Jon's willing to give his life to destroy the ritual. Marks 8 and 9 (Stranger and End) are purely altruistic on his part.
and from there on out, he continues to only get Marked via Protecting People.
Slaughter's from saving Melanie. Flesh and Buried are from saving Daisy. Dark is from trying to stop yet another ritual, something that he still believes could potentially end the world. Lonely is from saving Martin.
[this brings the final count to an exactly even split; 7 from external forces, 7 from Jon's attempts at protecting people]
as Jon becomes less and less human, he tries to save more and more people. and he's willing to give his life to do so!! he's willing to die!
and he succeeds. he successfully managed to save all his friends. it only cost him the world.
