Yeah, there was no answer for prime Shaq back in the late 90s and early 2000s when the center position was actually valued and guys were still allowed to play physical, hand-check, etc.
With the way everyone has gone to small ball, Shaq would literally break teams down now. That includes the current Spurs squad. Does anyone really think Poeltl or Eubanks would be able to do anything to stop Shaq?
That said, old & busted Shaq (from his late Miami, Phoenix, Cleveland days) wasn't the same force on offense and would get roasted on defense. His peak was crazy, but he fell off the cliff hard.