This video is also a nice addition to the topic:
https://www.youtube.com/watch?v=ca0NBLDtRjU
It brings up valid points on why swords and hilts had such disparate lengths through the late middle ages and renaissance, with advantages and disadvantages.
A good takeaway generally is: large swords with long hilts and blades employ different parts of biomechanics on the cut. They need more twist in hips and body. This would, in my opinion, apply to most of the Feders we have, where we have handles that could easily fit three hands and then some without grasping the pommel.
If we go down the (in my eyes dubious) "pictures as evidence" route we get different results from different eras and masters:
This is what we see in Renaissance treatises: some of Vadi's plates show both grasping the pommel as well as very long hilts (e.g.
https://upload.wikimedia.org/wikipedia/commons/2/29/Cod.1324_16r.jpg ,
https://upload.wikimedia.org/wikipedia/commons/8/8f/Cod.1324_17v.jpg ,
https://upload.wikimedia.org/wikipedia/commons/a/ad/Cod.1324_18r.jpg ,
https://upload.wikimedia.org/wikipedia/commons/6/61/Cod.1324_19r.jpg ,
https://upload.wikimedia.org/wikipedia/commons/9/90/Cod.1324_19v.jpg )
The "Fior de Battaglia", on the other hand, mostly shows shorter hilts. It is a much older treatise, so I would argue that this is to be expected. In the rare instances where a long hilt is shown it, to my eyes, seems slightly distorted. What IS shown a lot in the plates, however, is grasping the pommel, regardless of hilt length or (as far as I can tell) pommel shape. Some of the techniques, especially in the close plays section, are greatly facilitated (or rather: should only be applied) if there is a gap between the opponents hands, either through a long handle or when they are grasping the pommel. (e.g. Sword in Two Hands [38], [50], [57], [60] on this page
http://wiktenauer.com/wiki/Fiore_de%27i_Liberi )
The images in the Goliath Fechtbuch's Longsword gloss look severely out of proportion: in many of the images the swords are drawn to be as tall as the men holding them. At 150cm length (a very very very cautious estimate for the length relative to the persons shown) we are hardly talking about a longsword that can be worn, carried and quickly drawn anymore. Sure, it is about 120 years removed from Fiore, but I don't see evidence in surviving examples that typical longswords were as tall as a man by the early 16th century.
Generally I don't think historical artwork and drawings are something we can draw definitive conclusions from.