I used to think this but it only seems to be true for a shallow tech advantage, which isn’t this scenario. A sufficiently deep stack of compounded tech is robust against even aggressive talent poaching. The knowledge is embedded in the network, not the random individual.
We see this in jet engines, silicon fab, et al.
I mean, even north korea has figured out the nuclear bomb, the original greatest secret deep stack of compounded tech. Seems like anyone can figure out anything if they are hell bent on it on this earth. Engineers seem to be more fungible than people anticipate I guess, and no one really comes up with unprecedented unique ideas. The whole research process incentivizes incremental work on known concepts to justify receiving funding at all, since it is in high demand and short supply.