Hi drex,
Neither is inferior. it is a matter of preference. Most Nationals are bottom bee space and if bought as top space are usually a bit more expensive (manufacturing numbers game). Langstroths were top bee space as the norm.
Like everyone else (at least nearly everyone else) I started with bottom bee space with Nationals and WBCs, but was soon aware of the alternative option, so apart from my first flat pack hive super which was nailed together all the rest of my boxes were screwed, which allowed a fairly easy change over. After I tried a brood with the top bee space I converted all mine to that format.
The frames are that few mm lower in the box to get them out, but, as you will find out, when putting the boxes back together the bees on the top of the frame bars would be relatively safe from being decapitated with a top space but are not with bottom space.
The crownboard only needs to be a flat sheet (I have put battens on one side of some to prevent warpage) so that is a simplification also.
Routing out the top does not fill in the space at the bottom, but that may be a minor detail.
I dont use castellations in any hive, which might have a bearing on which is preferable. Yes, I tried them and discarded them. I can (instantly) choose frame spacing in supers to suit me and I found removing frames to be so much easier without them.
A lot is preference and experience. I have tried a few different formats in my Nationals over the last 10 years. I am now reasonably settled on 14 x 12, top space and with OMFs. Reasons are space (and swarming), ease of operation and dry wintering (without worrying about too much, or too little, ventilation). Fits in with the Dartingtons as well.
Regards, RAB