I agree using the common definitions sweeteners could be called flavors. However the FDA has only approved sucralose as a non-nutritive sweetener which for regulatory purposes is a different category of ingredient than artificial flavors.

Approved artificial flavors: https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFR...

Approved artificial sweeteners: https://www.fda.gov/food/food-additives-petitions/additional...