I think they didn't put as much effort into the gameplay in this pack. To level up in spellcasting, you just spam the same grindy things over and over again. With vampires, you first got bit, had to wait 3 days, then went through a few days where your thirst need was CRAZY, you got a cute tutorial where Vlad kept creepin' on you for days, and all the while learning from the vampire that turned you and having a special "Master" and "Offspring" relationship with them.
For spellcasters, just talk to any sage, doesn't matter which one 'cuz there's no special relationship or anything like you could have with Vlad, just a quick discussion, and watch them pop a magic bubble to learn from them. Not to mention the quest to become a spellcaster takes maybe 2 minutes if you're playing on single speed. Then to gain spellcaster experience and learn new spells, just repeat the practice magic interaction. Maybe change it up by having your sim stir a cauldron for a couple hours instead, and finding plenty of potion ingredients is really easy at the nearby shops, not to mention it doesn't cost much ingredients to make potions in the first place. It's the same interaction over and over and over again.
With vampires, there was more incentive to train with your teacher. They would show you how to use powers, and teach you how to fight as a vampire. You also gained experience by eating other sims by force, using new powers on targets, and it integrated well with everyday activities. Studying vampire lore unlocked recipes, and you had to harvest and grow plants, then master the mixology skill to be able to cure yourself if you wanted to.
And with witches in Sims 3, you first just had to play with magic, then you learned how to conjure apples and turn seeds into another type of collectable that would be useful to your alchemy. You had to search the world for rare seeds, or spend hours trying to convert a fish into a rare special seed. And even then, you didn't know what plant it would be when it grew up. You had to grow and collect your own potion ingredients, or send a dog or werewolf out to hunt gems for you, and the amount of ingredients you could buy from the elixer store was a lot more limited than the Caster's Alley shops.
If you studied hard, you would then be able to turn a sim into a toad-sim, not a random unmovable object, but that sim would go about their day all green with a frog head. You could raise zombies to life or turn a living sim into a zombie. Or dedicate your life to healing the zombies other witches created. If you wanted to cure all your needs with magic you had to practice your magic for a long time, and you didn't have to use the same play with magic interaction to do so. Casting your spells normally would raise your hidden magic skill. You could just be trying to convert a seed into something you need for alchemy and unlock zombification in the process. You're also more limited on how many spells you can cast before you have to rest and restore your mana.
Also, Sims 3 had a fortune telling career. And if you bought the extra fortune telling crystal ball from the sims 3 store and installed it, then it would raise your hidden magic skill as you used it. Your sim wasn't just doing magic for the sake of learning magic. You could be a healer, an evil witch, a fortune teller, or a fortune telling scammer. And that fortune career required you to meet with your clients outside of the rabbit hole work hours too and read their fortunes to them on your own time.
Spellcasters in the Sims 4 is too easy and too grindy, and there's not a lot to do. They spent more effort making a pretty voidy world thing and cut back on in-depth gameplay that actually integrates into everyday life. It makes me really upset too because I've been waiting SO LONG for new occults since vampires, and mermaids are just downgraded aliens and spellcasters were done so dirty.