I see the logic in that. The sheer number of stars near the center is so high that it increases the odds of them forming there plus they combine being so close together. Relatively speaking. Still I have to think then that super massive black holes aren’t formed from single star collapses or there would still be mini-centers scattered around the galaxy. I could see an explanation that after much time the center black hole becomes so massive that nothing in the periphery effects the whole significantly. But there should be quite a difference in younger galaxies. We should also see smaller black holes being drug across the galaxy towards the center creating a pattern like a comet by its gravity creating disarray amongst stars in or near its path.
Why? The black hole retains the angular momentum and vector of the original stellar mass. Admittedly they have huge footprints and can disrupt systems, but they would orbit the galaxy similar to the ways stars orbit the galaxy. Out in our neck of the woods the closest star is 4.26 ly away (Prox centauri). Even a 10 solar mass black hole at that distance is not going to do anything to our solar system.
Space is mind bogglingly huge compared to the matter in it.
Sun: Child's Soccer ball (8 inch diameter)
Earth: peppercorn
Pluto: pinhead
Distance from Soccer ball(sun) to peppercorn (Earth): 26 yards.
Distance from Soccerball (sun)to pinhead (Pluto): 1019 yards
Distance from Soccerball (sun) to another soccerball (Alpha Centauri) : 4000 MILES (or NYC to Berlin)