I feel like it comes down to playstyle. Players who like to blob into retreat paths or don't have as good micro probably favor Fusies due G43s better moving Acc and the 6th model meaning you are punished less for late retreats. The extra sight/flares also isn't nothing if you're playing against MG spam and need the extra sight for flanks. I always build at least 1 Volk for sandbags - never go full Fusies IMO.
I think the unit has changed a lot since the original topic of this discussion was brought up. I have seen people use them as a complete mainline replacement of volksgrenadiers, or, like you said, use a mix of the two together. And that is a good point the usefulness of volks being able to place sandbags
Correct me if I am wrong, but if you go full volks instead of full panzerfus then you have better early game power, but if you replace volks as your mainline with panzerfus you are trading some early game power with better late game scaling and long ranged power?