Am I just having terrible luck with ascension skill books or did they lower the drop rate since the last patch? So far, I've only got 1 yellow skill book since the server came online after the last maintenance, compared to about 2 to 3 per day prior.

Low drop rate, they covered that in the patch notes. You’ll get regular skill books for days but the yellow ones are only in certain locations and low drop rate for whatever reason.

It’s ridiculous, I know

I understand that the it's considered a "rare" drop but what I'm trying to say is that the drop rate seems lower now compared to how it was before the last maintenance. As I've said, I used to get about 2 to 3 or at least 1 per day before the last maintenance, but now I've only got 2 since yhe maintenance, that's 2 drops in 5 days of grind.

As you have probably noticed, they patch and remove certain things from the game or nerf them the point of absurd rarity, i.e., Ascension skillbooks, armor, and other loot table listings that never seem to drop. Mark my words, every time the community sees a drastic decrease of an in game item, it will immediately become available on the Pearl shop in so many ways. PA recently nerfed red spoils chests so you can't farm Violents efficiently to get ancient tablet's, boss stamps, or grand stones. Then they tell us it was beoken, but gave us a hot time event with broken spoons, but launched a hot deal to purchse with $$$. After that patch, all items are constantly flashed as hot deals, but you can't farm with certainty anymore. Whales keep the game moving though, so not much room for me complain. I'm not f2p, I support the game by micro purchases, but RNG doesn't favor those without substantial capital. My two cents.

You will see it happen again!