Who said “ flat freq response “ is the best?

Your missing something!!

With multiple drivers the crossover from the tweeter to the mid/bass is critical. Often its hardly ever smooth enough. Too many issues with dispersion, plus the mid starts to struggle as all drive units tend to break up badly at their extremes.

With treble units its usually at the low end where a lot of male voices are.

@elizabeth ,  I think you are absolutely, and without any doubt in my mind, 1000% correct!!!

Easier said than done sometimes maybe...but not impossible (if you don't confine yourself only to the most immediate possible causes and are persistent). And that will pay ever bigger dividends the further one can take it - even if someone decides to take it past the point where they feel it may already be 'good enough' - always plenty of unrealized rewards to be mined there.

In a room no system is measuring flat you have to go to heroic efforts to even get close. Aiming for flat from a design perspective is so end user has a known base to work from still many designs do not aim for flat response adding more variables to system synergy. Since massive variables exist every audio system sounds and would measure differently depending on these variations.