I’ll say it depends on where the comparison is made. In a vehicle having the tweets separate gives depth to the sound stage. Different vehicles have different layouts sometimes making it challenging to get the best sound. If you’re driving a 70 chevelle go for 3ways in the front doors and 2ways on the back deck. Almost all vehicles having separate components are replaceable w better ones of the same size. Example.
If you were outside, cut a hole in plywood and mounted a 6.5 full range then compared a 6.5 w a tweeter next to it, stood there trying to decipher a difference in sq it’d be hard. In a vehicle if the full range is blaring into your knee you definitely lose some highs of the tweeter. Having the tweeter higher and reflecting sound off the windshield or coming from either side the sound is free to hit your ear holes.