are 47re autos weak?

I'm not sure actual 47's WERE used behind magnums. The number indicates power level, so 46 is lower power level than 47 or 48. V10 and Cummins output a LOT of torque are installed in VERY heavy vehicles designed to tow and carry heavy loads. So right out of the gate they see heavy use. Maybe "Ma" should have put allisons in them...........or just stood firm and insisted people learn to drive 5 speeds.

And people can tear up a lot of hardware from ignorance, too

And they aren't just a "727." 727's had many power levels and WERE different between 318 or hemi and changed over the years. A parallel might be applied to the "lowly" Powerglide. When I was a kid I wouldn't give you 3 bucks for a damn Powerglide, yet today, built with heavy duty aftermarket parts, they are drag raced with tremdendous power, over 1000hp in some cars