WOW, applying four coats of finish is never a good thing, if he had used an acrylic primer/sealer two coats of finish would have done the trick
Now, this got me thinking, and I realized that it is possible that your walls were sealed just fine, but he used a
designer paint - even after priming, designer paints
can take many coats to achieve coverage, depending on certain factors.
But I tend to believe those walls were, in fact, too porous to apply finish paint.