I've been through a couple dozen deathclaw attacks by now, several back-to-back. Bethesda claims that they are increased by two things (1) general foot-traffic leading to your vault door, such as an increased influx of dwellers caused by radio room(s), and (2) the frequency with which you open the vault door.
Pretty much every time I log in (for an average of 5-10 minutes), I get at least one attack. But, every time I log in, I am (1) letting someone in called by the radio, (2) letting them out again to go die in the wasteland, and (3) usually opening and closing the vault door several more times to either let in or out explorers. So there it is. If you go full shut-in and hide, you should see less of them.
Status-wise, I have 155 dwellers and a bunch of rooms. Every last dweller in the first three occupied rooms (6 each in 3x3 nuclear reactors) is level 50, perfect 10 SPECIAL, and armed with legendary armor and weapons (mostly top-tier power armor and all 20+ weapons). Yes, I have opened many, many lunchboxes. I have also likely killed (as in sent to the wasteland to die) hundreds, if not a thousand+, dwellers in order to artificially cap my population at 155.
The first time I got hit by deathclaws, they killed 3 folks in the first room and three folks in the second room, (for a total of six, for those of you into advanced math) before they were put down in the third. Which is a surprising lot of death, considering each and every one of them was -- very literally -- the best and strongest dweller currently possible in every metric the game allows. I am relatively sure, however, that the dwellers in both of those rooms started at approximately half health. I have no idea why, but that seems to have been the case. I've concluded that the game just decided to stick it to me for the first one, to drive things home and make it more of an "event." Which is kinda cool, but really only cool because it happened only just the one time....
Every time since that first deathclaw attack, I haven't lost a single dweller. I do babysit and apply stims. But I always miss 1-2 entirely, and they have always survived -- although usually just barely. Usually put 2 deathclaws down in the first room, and then the remaining 2-3 down in the second. They haven't made it past the second since that first time. Two back-to-back attacks would kill a lot of people in my vault if I didn't stim everyone back up to max after every attack. Which I do, because I've been hit with back-to-back attacks.
I have to assume that their power scales in accordance to something, for the simple reason that the things that tear through me would be unstopable by anything less than max/max+ dwellers.
So, there you have it. One anecdotal take on deathclaws from the max-everything end of the spectrum. They scale. They hit hard. After the first time, they seem to hit considerably less hard. Them's the breaks, and gotta be realistic about these things, might as well make the best of it.