I'm not going to quote the whole above, but I think some good points are raised.
we do know is that Giannis' +/- data right now is likely inflated due to how well Milwaukee's supporting cast fits around him while Duncan and Garnett had very robust portfolios in a multitude of circumstances
I think this is an important point to raise. Although people often rightly note how Duncan had Manu, Parker and Robinson as great complementary pieces, in 02-03 I think he showed his ability to shoulder the load of a championship team on both ends. Lifting on both ends when the playoffs roll around, and winning a ring with a sophomore TP, rookie Manu and a 37 year old Admiral.
However, I think it's an even more important point regarding KG. He was year after year the victim of a mismanaged and miscoached team. Compare this to Giannis, who has a stud All-Star piece who doesn't need much of the ball, and a whole raft of other complementary pieces, and I think you get a more accurate representation of the picture.
Giannis' situation more aligns with Timmy's - great roster building and coaching, and very steady.
KG could only dream of such a thing, and once he got it (despite being past his prime) he was able to anchor a historic defence and be a top-3 player in the league.
I think Giannis right now is a better offensive force than Tim Duncan ever was, as he's so deadly scoring the ball and is a great passer for his size and position. However, I don't think he's better than KG on offence.
The thing that really for my mind holds Giannis back is playoff performance. Duncan obviously won a handful of rings, and was a playoff beast year after year. Once KG got his legs under him his playoff performances were awesome (I'm talking 2001-2013, but especially 01-04). Giannis has 2 years in a row now of somewhat underwhelming playoff performances, especially series' against Toronto in 2019.