To be honest, the way we were taught to defend our beliefs was meant to deal with the everyday person who knew very little about Christianity or the Bible. I can recall many times that I was challenged on my beliefs and was easily able to parry any approach by using the texts taught to me and that I could find in the Reasoning book.
But my ability to defend JW beliefs would have been strained had I run into anyone who understood those beliefs or had a reasonable grasp of the Bible. If JWs are having trouble defending their beliefs today, the Internet might be the biggest reason for it. People can develop a very effective criticism of JW beliefs by watching a few videos or reading a few messages online.
I don't really think the way that JWs are prepared has really changed all that much. But they are facing a world that is better prepared to respond to them and to attack their beliefs.