WebView is a simple way to embed content in an application, but it runs in a sandbox, could become outdated, and offers limited capability. CCTs on the other hand, have more advanced features such as customizing the appearance and interface elements, like the toolbar and menus. They are also significantly faster, can send callbacks to the application, and share cookies and autocomplete data with the browser, considerably improving the end user's experience. The main drawback with them is the URL bar they show at the top of the page, making them look like websites that aren't a native part of the app.
TWAs are similar to CCTs in terms of feature, as they're also based on Chrome, but open in full screen and don't display the URL, which is a convenient way for programmers to make the end user experience more seamless. They offer the same functionalities as Custom Tabs but have to respect stricter guidelines: The app and the content in a TWA have to be from the same developer, comply with the Play Store policy and PWA installability criteria, and load quickly. Trusted Web Activities are available for people running Chrome 72 and above, so most Android devices will be able to show these when developers implement them.
I'm glad Google is imposing these, as I'm particularly annoyed when an application directs me to an external webpage instead of opening content natively. While I understand this is sometimes a necessity, there are still too many companies that only implement a few features in their mobile apps and open their site when you need to perform more complex tasks.