The hell is with that timing.... why the eff is he just throwing out recipes and ideas now?? Just wait for the right moment and then release them at a good pace...
I think the main disconnect is that japanese mayo is very distinct in flavor (often called more "savory" and "brighter") compared to regular mayo. Japanese people often grow up using it as a condiment for cabbage/salad and virtually anything fried. It is something that they think of as necessary to any kitchen.
What these authors dont realize is that it is distinct because it is made differently (namely using rice vinegar vs distilled vinegar) and these isekai don't take that into account. Basically anywhere but Japan you wouldn't find anyone that resonates with the idea "obviously we need mayo"