PS: Are you aware that there are a number of risk levels used across the board in aviation regulation (except, generally speaking, in Australia) , not one single one to define "safe", as you suggest?
I presume you're referring to Minor, Major, Hazardous, and Catastrophic - with associated allowable probabilities of 10-3, 10-5, 10-7, and 10-9/hr, respectively. You are correct that 'safe' is not referred to in so many words, however it's commonly stated that if a system can meet the 10-9/requirement, then it's considered safe and you don't even need to address if the failure is Hazardous or Catastrophic.
The original FAA EROPS requirements were finalized in 1985 - and were soon used across the north Atlantic (granted, it's possible to fly across the north Atlantic using a 60 minute diversion using less than optimal routing - some operators chose to remain with 60 minutes or a strange pre-EROPS 90 minute 'exception' rather than jump through the hoops for full EROPS). I certainly don't remember the early rules as making " trans-Atlantic EROPS operations as close to impossible as possible" - although they were rather restrictive.