No, the War Powers Act does not constitute a return to isolationism. It has much more to do with the idea of separation of powers than it has to do with attempting to prevent the US from getting involved in foreign affairs. This is proven at least in part by the fact that the US has not noticeably turned towards isolationism in the 40 years since the act was passed.
The War Powers Act was passed largely because of concerns about the US getting involved in wars without Congressional consent. This was at a time when Americans were becoming worried about an “imperial presidency.” The act was meant mostly to rein in the president and give more power to Congress. In the years since, the US has intervened in many foreign issues. This is not the mark of an isolationist country.
The War Powers Act was not primarily meant to prevent the US from getting involved in foreign countries. Instead, it was about making sure that Congress had a say in such involvement. Because of the Vietnam War, many people in Congress felt that the presidency was getting too strong. They felt that the presidency had taken over Congress’s right to declare war. They felt that presidents were committing troops without asking for Congressional approval and they felt that this weakened Congress. This was the reason for the passage of the War Powers Act.
The War Powers Act did not bring about a new isolationism. The US remained strongly involved in international affairs. For example, just a few years later, the US was arming Afghan rebels who were fighting the Soviet invasion of their country. The US was not pulling back into a shell. Instead, Congress was simply trying to reassert its authority.