So it is ok to replace Grenadiers with Ostruppen or Assault Grenadiers, or replace Volksgrenadiers with Panzerfusiliers but British are not allowed to have a replacement to Infantry Sections? Why the Bias towards British?
Things like Pathfinders, Assault Sections and Assault Grenadiers are trade offs. They need to be used in a very specific way or don't have snares. Yes you can completely replace your mainline infantry with them, but it will be a risk and good players will seek to exploit that risk. Now we've all seen how bad it can be when a unit does all the same things the mainline infantry does but is straight up better at it and replaces them (Osttruppen). People would pick them every game. And with Raid Sections having a good all round profile that would make them easier to play with than the static IS, and with both not having snares anyways, the latter wouldn't be an unlikely scenario.