Wrong toe in/toe out would wear both tires the same. Too much toe out scuffs/wears from the inside to the outside. Too much toe in scuffs/wears from the outside to the inside. Could your worn R/F tire, just be low on pressure?
Once, both my fronts were wearing on the inside & the outside, dumb *** me, my 19" Firestones had only 12 Lbs pressure & didn't even look low or mushy!
Once Gregg couldn't push Vermin, with it's 16's up the driveway, tires didn't look low, you guessed it! pumped them up & ZOOM!!! Bill W.