Given that the rate of new dwellers via pregnancy vs radio room is staggeringly in favor of pregnancy, why is the radio room even necessary considering the risk (raider/deathclaw attacks) vs reward is completely unbalanced?
A well-staffed radio room helps boost the happiness of the population. Even if you're ignoring the newcomers it attracts (which I'm currently doing) it's useful if you have the power and guns to keep your fortress running.
While it is much faster to carry out breeding en-masse, the radio room is nice if you're just stopping in to collect resources and SPECIAL training, since you don't have to micro-manage your population, and you don't have to wait for newcomers to grow up before assigning them to a room.
Deathclaws aren't that big a deal if you have a reasonably large, armed population. They don't stay in one room long enough to kill a dweller (the first time they go through your vault), so as long as you can kill them before they reach the end and start looping back you'll be fine. The only remaining danger is that incidents will occur while your dwellers are still on low health.
I have a 6-person room just by the door, and nobody in the double storage rooms/living quarters on the top couple of floors. This means that any invaders will only encounter 6 dwellers at a time for the first 4 or 5 rooms. These rooms have priority (after my wasteland wanderers) for good weapons. Raiders don't make it past my first room (6 dwellers in a Nuka Cola Bottler with enhanced sawed-off shotguns), and deathclaws don't make it past my 4th inhabited room.
Because of these security measures, I keep my radio room fully staffed and I'm currently sitting at around 93-94% happiness.