I wouldnt say most FVNs focus on sub bottoms, merely bottoming is not the same.
Those parts that possibly shocked you are likely because this FVN is more specialized for sub bottom readers with specific tropes, situations and even words that are designed specifically for us and arent as common in most fvns where the MC merely bottoms.
I really enjoy this FVN as a sub bottom cuz its not trying to please everyone and knows their audience, many fvns have the MC give very strong bottom vibes but also dont want to make him an easily manipulated pushover so they try balance him by having him throw some temper tantrums on occasions which just...doesnt really balance things, usually makes it feel more like a manchild than a more vers/dom individual. So i would just say it can often be more of a writing problem.
Plus the main husbando in those fvns is often some inexperienced clueless guy who doesnt even understand his own feelings which is very far from the strong reliable individual presence Ranzkai has, they are very different.