Mario kart: Yeah, that chunky seat tube should not have any impact on your saddle setback. Seat tube angle is measured in middle of seatpost kind of no mather how thick seatpost is, but I think Patrick mentioned in video that Velobuild have 72° seat tube angle and Scot has 73°, but Velobuild according to their website geochart has 74° witch is pretty noticeable diference, maybe that geochart that Partick was looking at is not correct.
That bike looks pretty good, but men that frame hitting rear derailleur is pretty big oversight.
PS: difference between 74° and 73° at 750mm saddle height is 12.5mm and if he has higher saddle height difference will be even bigger, so Patrick needs to have saddle 13mm further back on Velobuild compare to Scott witch I think checks out.
PPS: attached geochart from official Velobuild website.