What the others said. Many of the spells are either basic cheats, or reskinned content from other packs. But there are some other things I'd like to call out.
Potions are a mess. They're not worth the price it costs to make them, or worth the effort it takes to get their ingredients. It's not worth selling them. Only a couple of potions are useful, and Plentiful Needs is way too easy to make and unlock, for something that's so powerful.
Familiars are also useless. They're glorified drones that sometimes give you generic pop-up messages. You can't interact with them besides choosing to summon or disperse them. They save you from death by magical overload, but magical overload is something you have to actively go out of your way to achieve, and it's even harder to die by it.
Brooms basically teleport you. You can't ride around and have fun with them, which gives them less immersion and gameplay potential. Duels are similar, in that there's not a lot of interactivity or variation.
They're also almost completely unnoticeable if you're not playing with them. At least werewolves can wolf out sometimes, and vampires fear sunlight. Witches might ride brooms if you give them one, but other than that, they don't cast spells or do anything magical autonomously. And if you try to have that via the club system, they just cast Inferniate and burn all your stuff. So it becomes a detriment to try and work with them.
They also have no secondary form, which is a major appeal for vampires and werewolves. You can greatly customize them. Not that you could do much with spellcasters though, since they have very little CASsets that fit the spellcaster theme. The only witch hat we got was in a completely different pack.
On top of that, what makes them different from other sims? Vampires and werewolves require you to change up your gameplay style to accommodate them. Mermaids benefit from living in worlds with swimmable waters. Spellcasters are normal sims that can sometimes use cheats if you feel like it. And I get that witches are generally portrayed as enhanced humans, so there's less room for deviation from normal sims. But there's little incentive to play them outside of that way.
I love playing spellcasters, but they're pretty basic. I have to imagine a lot of my stories and gameplay because RoM didn't give us enough to work with. Meanwhile, werewolves and vampires have unique looks, unique items, and unique gameplay.
