... The Elantra does get the deeper trunk.....
Unless VW nuked this feature in the current GTIs and I didn't notice, the cargo floor in the GTI is adjustable and can be lowered by about 3 inch (making it noticeably deeper). The picture in the article shows the cargo floor in the raised position.
Another notable thing about the latest GTIs (not mentioned in the article) is that VW decided to make standard on all GTIs what used to be a $3000 stand-alone Performance Package back in 2015-2016 (locking front diff, bigger breaks, suspension tweaks, dynamic chassis control, etc). Consequently the prices went up across the board considerably plus they removed other features that used to be standard on certain trims (e.g. BLIS w/cross traffic alert, Auto High Beam on Autobahn) and cheapened out on some interior trim pieces. The only upgrade, now standard across the trims, is the 8" display which used to be part of the Tech Package back in 2016.