Do not go and tell him straight on his face that you feel he has taken a wrong turn. No leader wants to hear that. You can give him tips as to how using design patterns will help him out.
If you want to use this technique, you need classes that fulfil four basic roles. You already implement three of these four roles by following the dependency inversion principle. The service and the client are the two classes between which the dependency inversion principle intends to remove the dependency by introducing an interface. As you can see, dependency injection is a great fit for applications that follow the dependency inversion principle.
You can read more here: https://stackify.com/dependency-injection/
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath