Atm, they seem like a waste of popcap, having 4x volks and 1x jli is not better than having just 4x volks and saving the popcap for a useful unit. The stealth and infiltration isn't really useful as it doesn't allow you to flank with them and infiltration is not good as they cant really do anything alone anyway. They seem to lose to everything, if both are in green cover.
All of this is just my personal experience, perhaps there is the same problem with pathfinders as I never see them used either. In two months of playing(almost), I have never seen anyone use either unit. Or perhaps the problem is my lack of skill, but I really like the unit but I can never make them work, I also don't want to use the Breakthrough doctrine instead as I don't like the blob encouraging playstyle.
As sanders said they are getting a vet requirement buff so it shouldn't impossible to vet them up like it is now, should help them a lot in scaling, Also if you manage to pick up a lmg off the ground they turn into pretty good elites. The biggest issue is that this doesn't happen often.
JLI use to get used a lot back when Scav Doc as a whole was good. Now there isn't really a point in going Scav Doc when the Ostwind is meh and there are better options for Elite infantry (Obers or Falls) rather than JLI.
Next patch thats coming next week I think should help them be more relevant. So maybe we will see them more.