I agree, on the enthusiasm for pumice, I feel that it is the one essential component of any pot-soil mix that I make, if I do not have pumice available (and it is surprisingly hard to get a decent prices in big enough quantities - for example it irks me that the big box stores tend to only have perlite) I tend to leave heavily pot bound plants in the pots they are in rather than repot them in soil with little or no pumice.
To try and provide some info why in my view pumice is such a great soil component: Pumice does one thing that regular coarser grit of the same size does not: it retains just a little water and tends to have very many tiny little cavities (vesicles for the geology minded among us), this combo would appear to be really conducive to development of the very fine roots which tend to get lost during barerooting (not always all, but generally a good portion get compromised). I frequently find that roots have so heavily attached themselves to pieces of pumice that I can only remove them by breaking the root, which I tend to not do. These cavities can also retain air as opposed to water helping with the general aeration of the soil, though when many of the cavities are intact it tends to make the pumice water buoyant which can be annoying if you are a heavy waterer like me, where over time all the pumice will rise to the top of the soil, while the rest of the soil descends to the bottom, which is not ideal.
Another thing to keep in mind that pumice is mostly volcanic glass, this form is highly unstable geologically speaking and the glass starts altering almost from the moment it gets erupted from the volcano (devitrification), this process makes a variety of elements more readily available to the roots than they would be if you were using similarly sized river gravel or crushed granite. A very similar process happens to what is sold as lava rock, which tends to be of more basaltic composition, and because of the high iron content oxidizes quite rapidly (turning lava rock from its more grey color to more reddish).
All that said, I agree with the general response here: if you bare root a plant it is going to take some time for the root mass to re-establish itself, you can probably help that along by finding the right soil, temperature, exposure, and watering conditions, but in most cases it will take some time. On top of that the however many days that a plant spent wrapped up in the darkness of a box probably will have driven it to dormancy, which is another factor aside from the potential lost of root mass that can make a plant slow to get going again.
