It's easy to deduce that those folks would be more interested in hard tech than any paint-by-numbers startup. I've worked at startups and well-established companies, and have found it surprising how easily really good engineers will turn down lucrative but uninteresting opportunities at well-established companies and how readily they'll take an "interesting" role for less or sometimes way less money.
As an aside, I’ve just re-read a Terry Pratchett novel and your description of the good engineers’ behavior made me think of Leonardo da Quirm :)
https://www.tandfonline.com/doi/abs/10.1080/00221546.1943.11...
To my mind that's an engineer whose curiosity is uninvested in the outcome of the exploratory work.
I've known good engineers and great engineers and to some degree, they were all like Leonardo da Quirm, though not all quite as naive.
This is easy. Offer relatively competitive TC with a real potential upside to the equity package and a work environment that's attractive. BigCorp is mired in politics and decision-making that's grounded in risk mitigation. Do something legitimately interesting and folks will come. Give them some agency and the ability to really get things done and they'll stay.