If drivers are time aligned in a multi-way system that will clearly be visible in the step response curve. (= there will be one peak at 0ms instead of multiple skewed peaks representing the time misalignment between the drivers)
If this is audible or not......
I used to have a number of multi-way speakers and when optimized they sounded better (more cohesive sound stage, and speakers 'disappearing')
But this is subjective of course
Search for step response in this forum to get to know more
I share your subjective take from my experience with multi-ways and rather precise time alignment.
As luck would have it, moments ago i did a quick indoor tune on my current project.....
here's the step and impulse, and a pict of the speaker....a 4-way MEH main for use with a sub
I absolutely love the sound i get from fine tuning time alignments, to that precision.
Everyone should hear it outdoors to fully appreciate it, i think..
Oh, by time alignment I mean a flat continuous phase trace across all driver sections, with time-of-flight removed from the measurement.
Constant delays, be they digital, analog, or simple geometric stacking of acoustic centers, are just a part of "time alignment"