Much of the morphology of languages with predominantly verbal affixation does in fact describe aspects of events and states, rather than persons and objects. Salient features of events and states (e.g. direction toward a goal, type of motion, nature of location, etc.) are seldom expressed consistently by inflectional affixes on verbs. They are expressed instead by a more derivational morphology, encoded on specific lexical items only when salient.
Standardized
IF morphological categories are marked on verbs rather than nouns, THEN they specify aspects of events and states rather than of persons and objects, and they are derivational rather than inflectional.
Certain categories marked on nominals (such as number, gender, case) have corresponding categories marked on verbs, yet the locus matters for details of the meaning of such categories. Much of what is specified by nominal morphology (e.g., number of participants by number) is implied by corresponding verbal morphology (e.g., distributive, iterative, joint-effort, number of occurrences, etc.). Counterevidence would be languages marking nominal categories such as number, gender, case on verbs, with exactly the same meaning these categories have when marked on nominals.
Certain categories marked on nominals (such as number, gender, case) have corresponding categories marked on verbs, yet the locus matters for details of the meaning of such categories. Much of what is specified by nominal morphology (e.g., number of participants by number) is implied by corresponding verbal morphology (e.g., distributive, iterative, joint-effort, number of occurrences, etc.). Counterevidence would be languages marking nominal categories such as number, gender, case on verbs, with exactly the same meaning these categories have when marked on nominals.