The simple answer is; it depends. In this case study, we will not compare Shopify and Odoo. As an Odoo ERP provider, we will describe our own experience using both.
If you are using Shopify efficiently and it's sufficient, stick to it. However, if your company is a startup, a growing company, and will ultimately need more services, Shopify remains perfect in the front-end but quickly becomes insufficient to manage the back-end such as inventory control, manufacturing operations, Bill of materials, Purchase Orders, Accounting, etc.
The patch work begins. Excel, more Excel, more more Excel. This is perfectly normal and perfectly OK because no mater what software you think you need you must be able to envision what you want.