In that case: An unmanned kamikaze ship still needs the mass and size of a capital ship, it needs sublight engines and a hyperdrive and it needs an advanced piloting system. It has to stay with the main fleet in case it’s needed, so it costs additional money to operate. Why not buy a regular ship for the same price, which is much more versatile and not limited to one single use? And don’t tell me “it’s just a joke”.
I’m pretty sure a small TIE Fighter could do some damage to the Rebel cruiser. And the PT droids, stupid as they were, could fly ships and some of them were actually ships. BB-8 seems to be able to operate a ship. And if the First Order has enough resources to build a planet sized Death Star, I believe they do have the money and infrastructure to maintain a couple of kamikaze droids and ships.
All in all the weaponized hyperspace aspect of the movie didn’t bother me as much because I don’t think an X-Wing would do much against a Star Destroyer for example, but I can see why some people would.