To add on to skill acquisition from someone who also got all the spells.
I wouldn't mind the chance remaining the same if you had a progress bar that went up each time you saw and killed the foe with the spell. At least then you'd always feel like you were progressing, it shouldn't be something like 99 but say for Primal level spells 50 attempts, it took me 250 for Garuda, it just didn't feel rewarding when I finally got it, not getting it 49 times would be fine as I knew I'd get it on the 50th it would feel like progression filling the bar and getting it early through RNG would then actually feel good.