You make no reference to taste ...how are they tasting ?
Id stop by weight , note time for sure , but dont let that be the factor that stops the pour ( or blonding IMHO )
Taste the shot I dint think anyone would advocate not adjusting grind or beverage weight without tasting , but if its 2-4 seconds out and tastes good , then I'm not sure what the problem is , with the coffee or the grinder .
Number are simply measure ( dose in and out ) you can't taste em , i agree , they do let you adjust based on something more quantifiable than lets say blonding . Blonding is still a measure , just not one I could simply repeat and get tasty shots , or use as a really useful communication point to other people .
All above is jut my opinion , if you can get blonding to work for you getting a balanced tasty cup each and every time , then all power to you . Personally I could not .