If there were a great number of particles in the oil that you could see with the naked eye, that is very abnormal and, if that's what you really saw, big trouble could be brewing. No insult there, just pointing out the possibility of misinterpretation. Go to the used oil analysis sections and you will find a few used oil analysis of factory fill oils. They are chock full of metal, sure, but too small or few to be seen by the naked eye.
Most of the break in takes place in the first 100 miles, so IMO, that first 500 mile dump is the important one. That's also the time when the Type I contamination (the dirt and manufacturing debris) can be flushed out. After that, the a short "severe service" interval followed by normal.
What I have gleaned on the long factory fill intervals is that, a) they are assembling engines better now, so they don't have to "wear in" as much and, b) they are much cleaner in manufacturing them. I have been on several engine lines in the past few years and compared to some I toured in the '80s, they are NASA clean rooms.
My last new car (a 2000 MY Honda we still have) got a 1000 mile FF change followed by a 3000 mile change. If today I had a new car that specified a normal first change, most likely I could not stop myself from doing an early change.... but I acknowledge it would be an emotional response. Intellectually, I can accept a longer interval, knowing what I know. But one side of my brain is resolute on the topic ... the other a quivering mass of jello, both vying to control the hands.