I have said it time & again you can not create a good field on a computer just the same way you cant walk or plan your games from them, you will always need to see it in the flesh.
Practically speaking, you're right.
However if your fields are designed in 3D, by someone who actually knows what different configurations of bunkers will play like, you have the possiblility of making some great fields. If the field designer does their job well, they will place the 3D camera behind each bunker, and see what they can see.
When i do 3D field design, i usually start with features i know will work. I have to admit that the millennium series fields are a bit unconventionial, and i wouldn't design any of them the way they have been done.
Personally i love designing xball fields, because after the fact we play them out for 20 points, and i get lots of feedback from the players. I use this experience to design new fields.
In addition, if the 3D fields are reproduced accuratly, you should be able to do a good amount of your field walking from the schematics.
For example, you should be able to see which bunkers you can shoot from the snake, and so on.
With the 1m square grids used on the astroturf in the millennium series, you should be able to reproduce a field design that is 100% accurate.
Practically speaking your statement was correct, but with more attention to detail, virtual field design and field walking could be possible in the future.