"has been moderately" is correct and usable in written English.
You can use it when you want to describe something that has been happening at an average or moderate level. For example: "The temperatures in my hometown have been moderately warm this summer."
Lately, it has been moderately gentrified as the coolest spot in the city centre.
So far, the launch has been moderately successful: 30,000 people have played the game in the past two weeks.
Most French people will leave an additional tip of around €2 if the service has been moderately good, more – around 15% – if it is exceptional.
After dissolving the mobile giant's US joint venture, his recycling of some funds into European cable TV assets has been moderately successful.
While the pacification programme has been moderately successful, with roughly half the favelas "retaken" by the police from gangsters, there has been little or no follow-up with sewers, water supply, streets and social infrastructure.
So far, authentication technology has been moderately resource intensive primarily due to the complexity of manual provisioning and supporting tokens making it primarily suited to higher risk individuals in large organisations.
They had been moderately valued, at about £40,000, but he is concerned about the impact of illicit excavations.
I like to think I have been moderately successful, thanks in no small part to my scientific training.
All would have been (moderately) reasonable assumptions to make based on the way the Jets thumped the Buffalo Bills, 48-28.
The Seahawks have been moderately successful, winning one Super Bowl (2014) in team history, and they have a regional fan base that extends from Montana to Alaska.
