I disagree. Pillaging is extremely effective.
The "mother of all pillaging"
is putting an archer on your opponents first source of bronze. This is extremely effective. Because all your opponent can build is archers or horses, if he is lucky.
If your stack of pikes and horses marches around the enemy cities, pillaging the towns and farms, it's actually quite the same, just later in the game. "Opponent has no money for research" = "opponent builds low-tech troops". Your stack of pikes and horses returns home and gets upgraded. But your enemy does not have the tech and does not have the money to upgrade his troops. -> You take the city. The war is won.
About outresearching... It is possible, I was outresearching my opponents late game on monarch level. In the middle ages it often
looks like being outresearched. But with free religion, representation, maybe mercantilism and a decent population it is possible to keep up.