It has been hard progressing lately, as I was still unhappy with the definition of grammar and what grammatical features as seen in litterature was. Then I hit some kind of breakthrough yesterday, at least something new that made me go haha. I saw certain classes of abstract concepts being so frequently used in combination with other concepts that their expression used either short words or become part of the word expressing the associated concept. These forms coexist with longer forms, that would be seen as obnoxiously convoluted in comparison. These short forms are called grammatical features, as if they belonged to some entity that would be grammar. But they're just these frequently used abstract concepts that have short forms in a given language. Turns out that a number of these frequently used concepts is similar across languages, which is not that surprising.
So far, this view holds.