I'm not a professional, but we have had soapstone counters for five years and no sealing was needed. We use soapstone wax instead of mineral oil, only because it lasts longer and is just a bit less messy, but otherwise produces the same effect--darkening the stone for a more even finish until it darkens naturally over time (which is what has happened to ours now at the 5 year point). It sounds to me like you have done your research, but if you want back up information, take a look at some of the major soapstone companies. None of them mentions sealing, and since soapstone does not stain or etch, sealing should not be necessary.

http://vermontsoapstone.com/caring-for-soapstone/

https://www.sierrasoapstone.com/soapstone/maintenance

Alberene Soapstone answers the question about sealants directly in its FAQ page:

"No sealants are required to protect soapstone from spills and stains, since the stone is extremely nonporous. Some people do choose to apply mineral oil or food-grade wax for a darker look, but many prefer allowing soapstone to age naturally."

Best of luck. We absolutely love ours.