The thing is, back then, it worked, because every app looked completely different from each other, and so it was a clusterfuck anyway :-D
So, same thing as today then?
Yes, except it was much more colorful and vibrant. We had pixel art instead of the the deliberately-monochromatic committee-directed stick-figure horrors of today.
Correct, nowadays it's accidental and boring inconsistencies, because they're all trying to be more minimal than the other app.
Hmm… my memory may not be the best but apart from WinAmp almost every other app kinda stuck to the OS? ;o