Greg was monstrously strong, no doubt, but there can be a big difference between gym/bodybuilding strong, and meet strong. For instance, what could Greg squat? Just because someone can leg press 9,000 plates doesn't mean "squat" when it comes to free-bar squatting. And Kovacs could bent-row 4-500 pounds, sure, but ... again, this doesn't mean he could stand (deadlift) with world-class numbers.
If I had to guess, I'd say squats would have been his Achilles heel, if he had chosen to compete as a powerlifter. At the very least, the movement would have likely been the one to require the most attention and specific focus.
As with many large and accomplished bodybuilders, Greg was super strong on many machine and isolation-type exercises. Elite powerlifters are (working as) whole-body strong and have had years to train their bodies to operate as a single powerful entity. A machine that explodes as a precise and unified weapon.