The problem with evaluating the negative based on the emulsion side is that you are seeing reflected light only. So you are seeing only the surface of the emulsion, the rest of the emulsion may be undeveloped. Stopping development at this point will lead to thin negatives. This is why the base side is used since if you see a satisfactory image it means that the entire emulsion has been developed. Thus the warning to inspect the base side of the film. Every discussion of the technique that I have read always mentions doing this.
The idea that the oxidation products of the developer act as a desensitizer is very old. If the effect ever existed it would be dependent on the developing agent(s) used. I seriously doubt that the developing agents used now would have the same effect. The oxidation products of phenolic developing agents like pyrogallol are vastly different from those of a developer like Xtol.