are 47re autos weak?

47re's are mostly just 3spd 727, with an extra planetary hung off the back of the case, right? So why do they have the reputation as being weak? I mean I don't remember people complaining about weakness when 727's were behind 440's, or Hemi's, which weren't slouches. So why are the 47re's considered weak behind 5.9L magnums, or the v10's? please be as specific as possible.