That should be thalassocracy from the Greek thalassa (actually a loanword from the pre-Greek inhabitants of Greece).
You’re right, Blegen’s find at Pylos — literally on the first day of his dig there — meant there was a large body of published (undeciphered) Linear B texts for the first time, and that is what Ventris used. By the time he had his breakthrough, Evans had been dead for years, so he never had to eat crow about it. And thanks for the etymology!