VPC Transit Gateway was in the whitepaper "Amazon Virtual Private Cloud Connectivity Options", as was Transit VPC. However, this lesson only discusses Transit VPC (introduced in 2016) and not VPC Transit Gateway (introduced in 2018). Any plans to update the lesson?
Yes, we do have this update on the list. However, just remember that because AWS comes out with a new service, it doesn’t automatically mean that every use case will use that service.
Basically the difference is that a transit VPC is more of a network architecture concept while Transit Gateway is a service. Gateways can simplify your network but there are some reasons why a more traditional transit VPC. For example, some people don’t like the fact that a Transit Gateway is kind of a black box.
AWS will be the first to say there is no "best" way because of so many different variables. (See AWS Transit Gateway Tech Talk: https://www.youtube.com/watch?v=A_2qq9fFxVU). For the exam, it’s important to know the general use cases where a Transit VPC or a Transit Gateway might be used but I wouldn’t worry about which is "right".