Is is balanced to swap "Built for Success" for "Fey Ancestry"?

Question

I am looking to create a homebrew race for a Quadrone, and the best place to start is with an existing race. With that in mind I have found the Autognome (Astral Adventurer's Guide) and it has several features that I like, but is missing one key feature that I am looking for.

All Modrons in the Monster Manual have Axiomatic Mind which stops them being compelled to act against their nature, and the closest normal racial feat is probably Fey Ancestry which gives advantage on saves to avoid or end the charmed condition.

Is is balanced to swap Built for Success and Fey Ancestry on a one-for-one basis?

Fey Ancestry Advantage on saves to avoid or end the charmed condition

Built for Success Add a d4 to one attack, ability or save after seeing the d20 roll a number of times equal to proficiency

I am actually thinking that Built for Success is a little more powerful, since it affects anything, but it is also restricted time per day. However you don't tend to make that many charm saves in my experience.

I would have checked detect balance to get some input, but Autognome isn't on that list.

Bonus question: Would it make much difference if I made Fey Ancestry affect charm effects and anything similar that doesnt specify charm on a case-by-case basis as agreed with the DM? I can't think of any charm adjacent things off the top of my head, but a related example would be this question about the bodak and my updated trait would allow advantage if it were charm instead of fear.

Answer 1

It's not equivalent, but still balanced

There is an updated version of Detect Balance (2022) that includes the new races, albeit by a different maintainer, so I am not sure how well tested the scoring scheme for new features in there is; it lists Built for Success as worth 8 points, compared to Fey Ancestry's 2 points, so about 4 times as powerful, agreeing with your assessment that it is more powerful.

So swapping on a 1:1 basis would not be equivalent. On the other hand, the Autognome scores an overall 36 points, definitely in the top quartile. The average is somewhere around 30 points across all the races, so dropping it by 6 points would still leave the overall race balanced.

About the bonus question: anything that is determined on a case-by-case by the DM is hard to evaluate for us, as it entirely depends on the DM. With a strict DM who always says no, this has zero added value. With a maximally acommodating DM, who allows this against effects like the suggestion spell (which does not impose the charmed condition, but does not work on creatures immune to charm), it is going to be situationally useful, and would improve this, although not in a major way -- I'd guess at best by a point or so.