Khalil brings all of the issues related to fiqhi matters assuming the student already understands the background. This is why studying books like Ashal al Masalik, Aqrab al Masalik, Muqadimat al Amrousi, is so important before Khalil
Risala ibn Abi Zaid is not enough since it only brings the forms of the different issues of fiqh. The structure of the rulings, preconditions, pillars, exceptions, etc is not in the Risala and conceptualizing this is very important before Khalil.