A string of one year stints would be a huge red flag to me. I would have a hard time selling this person up as we don't hire FTE's to come and go in a span of 12 months. Too much churn kills you, I'd likely pass unless circumstances where extraordinary.
Of course I probably wouldn't know if a place passed on me because of that.
I wonder what the probability distribution for how much hirers weight "loyalty" or "stick-around-ness" looks like.
On the flip side, it's my responsibility to make sure that my engineers are happy in their position and weren't sold on a lie.
There is a huge difference between being able to fix bugs and being able to fix architecture problems. I needed at least a year before I was capable of the latter in SunOS, probably more than a year.
But maybe the people jumping every year are doing more grunt stuff and the ramp up doesn't take as long? I dunno, I'm mostly retired and sort of a dinosaur.
I work for one of the big 5 and thus use a lot of the tools I use are developed in house (also, there are lots of special technological requirements that I have to understand and work with).
I've been here a few years and am still learning loads about unique company specific things that save me time when I have to do similar things in the future. 1 year stints would definitely not look good to me.
Good process reduced this to the level that is practical, but reducing churn is an important key to managing the unavoidable cost due to this.