I did a similar analysis before going with Ikelite for my R5. No doubt Nauticam is a higher quality housing but you pay a lot for it. And while the Ikelite housings of 20 years ago were pretty rudimentary and clumsy, I think they've come a long ways and it was hard for me to justify minor ergonomic/size benefits as being worth that much money. All the critical things like shutter/back focus trigger position, effectiveness at keeping water out, durability, strobe compatibility, vacuum systems, etc... I think is basically a push between the two.
The biggest thing you're paying for with Nauticam is an aluminum housing in a smaller and more "glove-like" form factor with more electronic bells and whistles and a slightly more ergonomic button experience. And access to all their ports and accessories, which I guess could be a deciding factor if you have the $$$ to burn on them. They certainly have more ports, wet lenses, and so forth to choose from than Ikelite does, though they cost a small fortune.
Anyways, as a hobbyist I was fine going with Ikelite. If money was no object or I was a pro doing this for a living, yeah I think brands like Nauticam serve that market well.