The crime the ATF thought was being committed was installing M16a1 trigger groups into AR15 lowers. It is legal to own both but not to be 'installed'. If not caught in the act then it would be extremely difficult to prove the machine gun manufacturing charge. Stand-off and ask to serve the warrant when it was convenient for the Davidians would allow all the time in the world to alter any select fire ARs back to civilian form.
So the initial warrant service was both amateurish AND excessive???? Seems more like a pick one or the other kind of deal.