This is not to say that markets have lost their price discovery function. Just consider the large swings in yields we have seen over the past two years, and the changing constellation of intra euro area spreads. The APP has not suppressed market discipline.
But what stock effects do is shield financial conditions from unwanted tightening forces and thereby help preserve the financial conditions that are needed to ensure a sustained convergence path of inflation towards levels that are below, but close to, 2%.