That was their intent. But my understanding is that DAK largely cannibalized the other parks when it opened because Disney didn't add to them as planned.At the end of the day, Disney wanted a fourth park because it makes people stay longer.
They could imitate California and pack all of WDWs attractions into two parks. The number of attractions across WDWs 4 parks are comparable to DLRs 2.
Indiana Jones Adventure in the MK won't make people add a fourth day to their visit, but Dinosaur in AK will.
Today, yes, the fourth gate likely causes people to stay longer.