That is exactly what is happening, and it's legal. It's very easy to hide profits and move them around.
However, insurance margins remain unaffected as the money did, in some sense, go out the door and is no longer in control by the insurer directly. It's not fraud. It's just anti-competivie self-dealing. So, no, it's not profits per se, but rather increased valuation via clever financial engineering.
A quick search shows me that on page 73 of Cigna’s 10-K, it clearly does not have its Express Scripts division accounted for in the “Investment Assets” section, based on how low those numbers are.
It just does not pass the smell test to me. The simpler answer, based on all the numbers, is that managed care organizations are squeezing other entities in the healthcare chain, but due to competitive pressure and upper profit margin limits due to ACA, they are not raking in big bucks.