Depends on the team you’re playing. Shaq would have struggled on defense against a lot of today’s bigs whereas Duncan and KG were far more versatile.How is Shaq not in anyone’s team? No one could stop peak Shaq. Duncan in the team makes KG redundant. Duncan with Shaq would be awesome.
I think Duncan/KG frontcourt is about as well-rounded as it gets and they would have co-existed well since Duncan did most of his work from low post and KG from high post. But both could obviously switch, as needed.