The only difference between residential…primary is the relative importance. trunk and motorway are different to the rest, though the difference is globally the same. Overall comparable to path vs. via_ferrata.
I’m talking about the mapper-perspective. You pick highway=path and add secondary tags as you think is necessary. If I’m not familiar with hiking, I don’t need to judge the suitability for hiking. With the pathway-concept I need to do be able to do this. If people not familiar with hiking judge a way by hiking criteria this will end up in a mess. The result is kind of random. Normal tourists might scramble where hiker just walk along.
highway=path can be “everything” and therefore might end up in a mess for the data-users, who only evaluate highway=*. But that’s not a mess. If I only evaluate boundary=* it will be a mess as well. 