Yeah, Yamaha's reply and what you experienced are consistent with how my previous Yamaha receiver worked. The front speaker levels are basically fixed, and then you adjust the center and surrounds to match. There's nothing wrong with this, unless you are also trying to insert a permanent bias to the left/right balance of the fronts (as opposed to using the balance control knob/buttons). It also assumes that you have enough adjustment range in the center and surrounds to bring them into matching levels.
You might feel subjectively that the fronts are too soft for a particular setting or position of the master volume knob, but there's no real problem as long as you are still able to get as much volume as you want, with it cranked up.
Older Yammies (maybe older than yours) also didn't have delay/distance adjustment between the fronts and center - just relative delay adjustment for the surrounds. Once they added distance/delay settings for the front and center speakers, they also added independent level adjustment for the front channels.