The phrase "a telling insight" is correct and usable in written English.
It can be used when referring to a significant or revealing understanding about a particular subject or situation.
Example: "Her analysis of the data provided a telling insight into the underlying issues affecting the project."
Alternatives: "a revealing observation" or "an illuminating perspective."
Last February the Everton boss gave a telling insight into his methodology on the training ground.
The way in which Wiggins reacted offers a telling insight into his changed mentality.
This, I think, is a telling insight into the changing relationship between reader and novel.
A recent study of contributions to India's political parties offered a telling insight into the nexus between politics and money.
That was arguably United's best effort and it came on 84 minutes, a telling insight into the level of their performance.
The concession inflamed the gathering — and offers a telling insight into the leadership style he may now bring to the papacy.
But as the state security apparatus remains intact — and willing to fight — and the government continues to count on support from Russia, the shift in mood in Damascus may prove to be a more telling insight into the government's fate.
The book offers telling insight on a topic that has ebbed and flowed across the world over the last 30 years, as governments of all stripes have set out to privatize state-owned enterprises and outsource services — what does the private sector do better than government, and what does it do worse?
Confidential surveys of water officials, water users and others involved with the Sacramento-San Joaquin Delta offer some telling insight on why the delta is stuck in a perpetual quagmire.
The more telling insight is that many of Trump's supporters will never abandon him; instead, more than a few will abandon the Republican Party.
Nietzsche's telling insight grew out of intellectual and cultural developments that had been unfolding for more than a century.
