It's a real position if the bespoke work produces something that stays inside the product after the engagement ends. It's a services business with a product attached if the bespoke work produces something that stays inside your team's time.
Test it directly. After the evaluation, the integration, the dev support, is the client's ongoing relationship with a product or with people? If the answer is that they keep calling an engineer when something breaks, or the routing only holds because someone keeps tuning it, that's professional services. The revenue scales with headcount and hours, not usage.
Developers, relationships, flexibility. Real assets, no argument there. But those describe a team's capability, not a product's moat. What's the thing a client keeps paying for in month six that they couldn't get by asking their own engineer to copy the configuration you built them in month one?