Sure! In the end, your current structure may be the best suitable compromise in your case anyway ... I'm just thinking aloud, without being able to offer any magic alternatives ... It is a challenge to make the menu nice and accessible, and I admit that the new mega menu had a certain impact on how I created the structure at mjau-mjau.com and even the for the default X3 release content.
Mega menu's all require a certain focus from the creator to strive towards a structure as suitable as possible for the mega menu. We do have additional mega menu extensions in store: 1)
A similar list grid, but integrated into a "Carousel" option so that the menu can contain an even heavier structure. 2) A subfolders grid (similar to a gallery grid, directly in the menu).
Just to note an undocumented setting for the mega menu list. This is how we have done it at mjau-mjau.com, because we needed to custom stack subfolders, and in what columns they displayed for the best overall balance:
The | character separates columns (4 columns), and the numbers represent the index of the child subfolders. With the above, we set child0 and 1 in first column, child4 and 5 in second column, child6 in 3rd column (because it has many child items), and child2, 3 and 7 in column 4 (because they had very few child items).