If the size of the flung-off objects is proportional to the size of the asteroid that may be the case, but it's also possible it's mainly proportional to the force of the deflecting impact. Regardless between a potential extinction-level impact and hundreds, even thousands, of smaller, "Hiroshima-sized" impacts, the latter would still be massively preferable. Statistically the majority would hit the ocean and do little to nothing as well.