I don't like comparing Giannis to Shaq. He is not as physically imposing as Shaq was. Giannis is closer to David Robinson minus the jump-shot and FT shooting.
He is not, but he is as dominant. bball-ref has shooting numbers starting with the 96-97 season. In Shaq's 3 Lakers title seasons from 0-3 feet he shot 77.1% and took 44.1% of his attempts from that range. The last 3 seasons from 0-3 feet Giannis is shooting 81% and is taking 44.5% of his shots from that range. In other words, Giannis shoots more from that range and hits at a much higher percentage than Shaq did at his apex. Shaq's best shooting season was 01 at 79.2% which carried his average those 3 seasons. In the last 3 years, Giannis has been 83.7, 80.8, and 79.1. There is a very strong argument that Giannis is the most dominant interior scorer that has ever played (I'd take Wilt over him, but I'm not sure I'd take anyone else). Even guys like Claxton, Gobert, Jordan, etc. that lead the league in FG% at around 70% haven't had a season from 0-3 feet shooting 83.7% (well Jordan just did that for the first time in Denver, but the volume isn't hardly anything).
I think a lot of people still remember Giannis as the skinny SF, but Giannis is a monster now and he is unstoppable in the paint. He isn't your typical old school big man in that he does spread out his other shots from all parts of the floor, but for pure dominance and volume around the basket, there is basically no one better that has ever played the game.