Hiring a coordinator is just like hiring any other legal expert to navigate regulations in your business. You hire an accountant to keep your books legal with the IRS, you hire a coordinator to keep your radio stuff legal with the FCC.
Sure you CAN do the IRS stuff on your own, but I would not go cherry picking regulations that do not apply to your situation and try to massage them to fit. Same thing applies with the FCC.
Simple things like renewalls can often be done without the help of those federal licensing service folks, but for initial licenses and most modifications, hiring someone to properly cross the Ts and dot the Is is how you do business. The time kludging through this on your own is much better spent growing your business.