I think cutaways and low decks help for all padle types, because the closer you plant it to the hull, the more efficient the catch phase. The cut away helps at the beginning of the stroke with all paddles. When I sit in a white water boat that ha sa high deck near the feet OR near my knees, it forces me to either assume a really tall vertical paddling position to plant the paddle close, or, to plant the paddle a couple of inches further away from the boat than I am used to. I can really feel both situations impact me negatively. Same for a GP in a sea kayak - I can hold it lower and plant it closer to the boat when the deck is lower and narrower.

Also, if the Euro paddle is NOT the tear-drop down-turned shape but is instead the type that is symmetrical or worse, has a really fat bottom half close to the shaft (whcih for some reason are most paddles for sea kayaks), I can really feel how that interferes with my stroke - it robs me from a couple of inches of closeness to the boat during the catch. See the wing paddle shape when seen from the front or rear - from the shaft towards the ends it does not have a bulge like for instance a Werner Ikelos has. One of the reasons I did not like the Ikelos when I had one (and don't like the Cyprus as much for the same reason) is that the bottom edge of the blade near the shaft sticks-out and messes with good form. Such shapes are not necessary for most situations and a tear-drop shape works much better for paddling. The only situations where such "fat" paddles work better than a downturned design seems to be in really shallow waters where other shapes can't scoop enough water as they hit bottom/rocks.

It is my understanding that catch cutaways and narrow catches are really only useful for use with a wing paddle.
The blade of a wing is placed as close as possible to the feet and moves away from the boat as it passes through the water. This can be seen in Kocho's clip. Euro paddles behave differently and do not neccessarily need the narrow catch placement as the blade moves more or less parallel to the side of the boat. Chalupsky And Barton's video, " the forward stroke" explains this well if I remember correctly.

Cutaways look cool but their functionality is limited with a euro paddle.