Custom permissions were recently introduced (FINALLY YAY!) to the enterprise version and nothing for the other plans, but I think this is a mistake.
Saap enterprise plans tend to focus on extra security, memory, support, automations and people included in the plan and are needed for very large companies in most cases. However, any serious small team, startup or small company do need custom permissions for managing their staff and guests but everything else included in the enterprise model is completely useless. There should some type of permission differences between the business model and the rest, it shouldn't be as white or black as it is now where the enterprise version is the only way to customize those permissions. Maybe make it so you have even more advanced permissions in enterprise vs business, but you need to include some of them in the business plan