I know that there are third party add-ons and snippets to populate fields on with answers from other fields but this really should be a core feature. Many standalone forms solutions like typeform & paperform already have this.
Thank you for the suggestion. I encourage other users to like your post or add their own comments to the feature request if they agree.
For reference, here are a couple paid plugins that offer this feature:
Gravity Wiz has an early-access perk called GP Populate Anything
Agreed, this would be a nice feature to have.