1) Who said the OP was intending to use d20 modern rules? It looks to me like they are seeking a 5e solution to their desired concept.
2) Mechanics does not equate to what a thing is. There is nothing inherent about the magic missile spell that makes it this way except that we typically agree on how it works. The mechanics can remain the same, but it can still be changed in ways that don't affect the mechanics yet allow the spell to more easily fit a person's concept. Magic missile can appear as invisible darts of force, screaming skulls blazing in hellfire, or rocket fists that return to the user after the hit. These all change they way the spell feels, without altering the mechanics. This is not laziness. This is a viable solution to creating a concept, and one that is less likely to cause issues since you are not changing or adding anything new into the game, hence there are no concerns regarding balance when using this approach.
3) Yes, a horse moves differently than a motorcylce. But last I checked, 5e is not so simulationist in its approach that different modes of land movement need to be differentiated. Yes, a motorcycle is smaller than a horse, but the difference is not significant enough to make a difference with regards to size categories (a 4 foot tall dwarf and 7 and a half foot tall goliath are both considered medium sized creatures). And no, a motorcycle would not have a kick attack perhaps. But that attack can be reflavored in any number of ways to be more appropriate.
4) Don't assume there is one path to achieving a concept in D&D, or that any particular path is "correct" or diminish the contributions of those that offer suggestions. Besides, outside of calling my option lazy and suggesting some vague d20 modern rules, I didn't see you offer any concrete way of executing on the OP's concept. Easy to critique others when you don't have anything to offer as an alternative.
