The licensing fees for open source systems are indeed low, but hidden costs lurk in three places: the manpower investment for secondary development, the responsibility for following up on security patches, and the adaptation work for vendor integration. When calculating the total cost, none of these three items can be overlooked.
The controllability of a custom system is irreplaceable, but a cycle of 8-16 weeks means the consumption of a market window. If the competitive landscape in the target market changes quickly, the cycle itself is a cost that must be factored in.
During the validation phase, use a standard solution to launch quickly, and after proving out the customer acquisition and retention model, upgrade to customization—this is the path that most clients have voted for with real money this year. What truly suffers on both ends is the "fast and fully customized" approach.