Frietas was a better fighter, and would win a clear decision. It took the pressure and power of a prime Corrales to beat Frietas, and Soto is NO Corrales by any stretch of the imagination. Soto's one of the most overrated fighters of recent years.
Popó was better.....Soto is only a known fighter because he didn´t face the best opponents, otherwise he would be a borderline jorneyman, I think. Popó had many faults, but he was a better fighter than Soto, no doubt in my mind.
Soto is a journeyman come good, someone who took his chance and had a good spell at the top (although if pac/jmm hadn't left he likely would never have gotten there) but he was always a hit and miss fighter, look how much trouble that thingy gave him, began with A, rios destroyed him, and he was not even half the pressure fighter that freitas could be.