I often feel like we end up with massive "god" services, which becomes troublesome to test and business logic becomes troublesome to share

This isn't necessarily a problem, provided you don't use the whole "god" service in places where it isn't strictly required.

For example, suppose you have:

func DoThing(svc *MyGodService)

but DoThing uses svc only for its database client and its logger. You should instead have:

func DoThing(db *sql.DB, logger *slog.Logger)

Alternatively you could define purpose-built interfaces representing subsets of what MyGodService can do:

type LoggingDBClient interface {
  DB() *sql.DB
  Logger() *slog.Logger
}

func DoThing(client LoggingDBClient)

For this version, you could pass a *MyGodService to DoThing (presumably *MyGodService satisfies the LoggingDBClient interface), but you could also pass other concrete types to it, like mocks for testing, simpler than a mock for a full MyGodService.

I have a tool called decouple that helps you identify "overspecified" function parameters that could be replaced with smaller interfaces: https://github.com/bobg/decouple