Nicely done Bastien.
The information is, as you point out, necessarily simplistic. To make it simple and universal, it loses nuance.
However that is just the level one needs when planning a long trip. You know that there will be bad-weather days, whatever time of year you travel, but you do want to know when the best probabilities are of reasonable weather.
Another point is that you have the basics that everyone needs. Beyond that the needs become more specialised and potentially confusing to those who don’t much need things such as daylength, ultraviolet levels and wind direction. Those three are useful to a person cycling through the countryside but of less relevance to someone staying in cities and travelling by train or plane from place-to-place. Those people may be keener to know when the key festivals are happening.
I plan using your app for the basic plan of some travel we are planning — working out when to go and in what order to visit the different places.