Are aberrations of CR 6 and below approximately as powerful as demons of CR 6 and below?

Question

Background

I'm currently playing a Great Old One (GOO) Pact of the Chain warlock in one homebrew campaign. Originally, I had designed the character to be evil and roleplay-heavy, with skill and spell emphasis on illusions and enchantments. He'd be mostly interested in just gaining power and influence under the radar.

Then, shortly before starting the campaign, the DM banned evil characters entirely. I still liked the concept, so I've been trying to tweak it. Turns out the campaign is also more combat-heavy than expected.

Currently I've got an Imp familiar, and was planning on trying out grabbing magic circle, summon greater demon, the Chains of Carceri eldritch invocation (which lets me cast hold monster at will on celestials, fiends, and elementals, once per long rest per creature), and so on. Give him a summoner/controller feel.

Thing is, I still want him to feel like a GOO warlock, so I'm interested in using a Gazer familiar instead of an Imp. Also, homebrewing Summon Greater Aberration (exact same as SGD, but for aberrations), and adding aberrations to the list of things Magic Circle and Chains of Carceri can affect.

Question

Are all aberrations of CR 6 and below approximately as powerful as demons of CR 6 and below? Or are there any outliers that would pose balance issues if I were to summon one via a summon greater demon-like homebrew spell?

Answer 1

Yes. Challenge Ratings Are Type Agnostic

The basic rules define challenge rating without respect to type:

A monster's challenge rating tells you how great a threat the monster is. An appropriately equipped and well-rested party of four adventurers should be able to defeat a monster that has a challenge rating equal to its level without suffering any deaths.

Consider Re-Skinning A Fiend

Keep the stat block and type for all mechanical intents and purposes. Have the description and thematic flavor be an aberration. This preserves the mechanical aspects of summon demon while allowing the story to have summoned aberrations.

Considerations for Summoning Different Type

Expectations

Monster types usually common characteristics about them. If the summoner was banking on getting a demon with the usual demon accouterments, switching it up could be an unpleasant surprise. Violating this expectation could be used as a storytelling mechanic.

Type Specific Spells

• Spells that affect fiends but not aberrations such as hallow, planar binding, forbiddence, and dispel evil and good would have a great change in utility if an aberration appeared instead of a fiend.
• Spells that can use type as a trigger e.g. glyph of warding would be affected.

Type Specific Abilities to Consider

• A ranger that has a favored enemy of fiends would be affected by having an aberration show up instead.

• The paladin's divine smite would not come into play against aberrations.

• A pact of the chain warlock would not be able to use Chains of Carceri on an aberration.