Is there a general rule about getting a benefit from feats that offer redundant abilities (from RAW, Sage Advice, UA, etc.)?
My specific scenario is considering the Arcanist feat from Unearthed Arcana: Feats for Skills:
Arcanist
You study the arcane arts, gaining the following benefits:
Increase your Intelligence score by 1, to a maximum of 20.
You gain proficiency in the Arcana skill. If you are already proficient in the skill, you add double your proficiency bonus to checks you make with it.
You learn the prestidigitation and detect magic spells. You can cast detect magic once without expending a spell slot, and you regain the ability to do so when you finish a long rest.
If you already have prestidigitation and/or detect magic, are these just nullified benefits?
I know the feat already addresses what happens if you have the Arcana skill, but I did not know if there was an overarching rule that I missed somewhere that would address this.