Is this the video you guys are talking about?
They showed 2 1ct diamonds next to each other and it's obvious that the Super ideal cut diamond looks bigger than the GIA triple exc one. Though the triple exc one might be the lower end of the exc range with a 63% depth.
The other diamond they compared was a 0.90 Super ideal and 1.01 GIA triple exc. This is where they both look similar in size.. not bigger.
Since when did anyone say that a 0.8 super ideal will look bigger than a 1?

0.8ct looking bigger than a 1ct sounds too exaggerated to me.
The point is that a superior cut diamond will look bigger AND more brilliant compared to one that is a less cut. Once again, I must say the comparision should be of fairer ground which is 0.9 vs. 1.0 and not 0.8..
If you consider the price point, a 1ct usually costs like 3k more than a 0.9ct, assuming the other color, clarity, etc. are the same.
It makes more sense to get a Super Ideal Cut 0.9ct than a 1ct GIA triple exc one, when the Super Ideal cut looks the same size, but sparklier, and cost cheaper.
Of cos I can't deny that 1ct sounds pretty awesome during discussion