"has been especially true" is correct and can be used in written English.
It can be used in the middle of a sentence to refer to a truth that has become even more accepted or important over time. For example: "The importance of regular exercise for maintaining good health has been especially true during the pandemic."
This has been especially true where China is concerned.
For this last set of occupations, this has been especially true in the past decade.
Most recently, that has been especially true with the weak housing data.
This has been especially true for highly leveraged companies in the junk bond market.
That has been especially true since President Richard M. Nixon removed the last vestiges of the gold standard.
That has been especially true in those countries that contribute the bulk of the non-American forces deployed there.
This may have been especially true in Stockholm, where there was a large German population.
Participants who agreed to an in depth interview may have been those who had a particular interest in advanced cancer patients and VTE – this may have been especially true of palliative medicine doctors and oncologists who see these patients on a frequent basis.
That has always been especially true in America, a country whose institutions — from the Senate to the Capitol — are explicitly modelled on those of the Roman Republic.
Regulation of consumer products moves slowly in the US, and that has proven to be especially true when it comes to chemicals.
(36-year-old with no education who delivered in a health centre 4 months ago) Several of the women who were interviewed that delivered more than 6 months ago said that they had problems remembering because they had delivered long ago, this was especially true if they had multiple checks: Look at me I have almost forgotten everything.
