Mirrorrorrim
Hero
There are lots of abilities that cannot be "taught." Not only can a Wizard not learn every spell in existence (there are arcane spells that are bard or warlock-specific, for example), but also not every magical ability is a spell.I understand what you're saying – you're boomeranging back to "PCs and monsters are designed different." But I'm actually being a bit more nuanced than what you're responding to, and I'd invite you to try to understanding this from a Player's perspective.
From the GM side of things, you're right. This uses monster maths. PC and monster mechanical stat blocks are designed "differently."
EDIT: I actually think there's more grey area within that & that in 5e it's not exactly on/off switch (either you're doing the tedious 3.5e way or you're doing the 4e way), but we can circle back to that later. Putting a pin in that for now.
I'm encouraging you to look at a scene with an Apprentice Wizard using Arcane Blast from the Player's perspective instead of the GM. That was the point of my wordy examples.
There are people who want every ability to be a quantifiable, PC-accessible option that fits their version of the lore. That's fine. If there are no rules for it, then make it up. But the "balance" of the rules objects in monster stat blocks are balanced for monsters who get to use them during an encounter before they are defeated, not necessarily for PCs who can use them over the course of the campaign.
Monster/PC ability separation is not wrong. But it is the rules and some people (and apparently the designers) prefer it. For example, certain humanoid monsters wielding normal weapons deal more damage per swing, and/or more often, than a PC warrior, but it doesn't mean that the PC warrior should be able learn how to make that exact same attack at that damage level.
Monster/PC ability parity is not wrong. But it isn't supported by the rules, even if some people prefer it. Make it up yourself. It's your game. But don't expect the "balance" to work exactly as is. It may well be superior to normal options if allowed to be used over the course of a campaign. But if you change the effect to be more balanced for a PC, then it still won't work like the monster ability. If you nerf the monster ability, it may well be truly "nerfed" to be less dangerous/effective than intended.