Someone else more experienced can correct me if I'm wrong, but it seems in line with how .NET Core is built. Less things are in .Core packages now and if you need more, you can add a package and use it in your code.

I think Microsoft does the same thing with .NET 5.

E.g. you have a Microsoft.Azure.Storage package and then if you need to use something that's not part of the Core, you install Microsoft.Azure.Storage.Extensions or something of the sort.

Yeah, you're right, and I'm not really opposing that way of doing things. What bothers me is that the Umbraco.Cms.Core namespace is being used all over the place, meaning that I have to install Umbraco.Cms.Infrastructure to get access to functionality within the Umbraco.Cms.Core namespace. That (to me) makes it very difficult to know what is where, and why. Might just be me.

In case it helps anyone with Umbraco 11. I had the same problem and ended up injecting the repository into the api controller.

[PluginController("globaltrade")]
[JsonCamelCaseFormatter]
public class BooksApiController : UmbracoAuthorizedJsonController, IBooksRepository
{
    private IBooksRepository booksRepository;
    private ILogger log;
    public BooksApiController( ILogger log, IBooksRepository booksRepository)

The repo has the ISCopeProvider injected and needs the Umbraco.Cms.Infrastructure package installed.

using Umbraco.Cms.Infrastructure.Scoping;

namespace JB.Backoffice.GlobalTrade
{
    public class BooksRepository :  IBooksRepository
    {
        private IScopeProvider _scopeProvider;
        public BooksRepository(IScopeProvider scopeProvider)
        {
            _scopeProvider= scopeProvider;
        }

To make this work you need to add the repo into the DI container during services configuration in the Startup.cs file i.e. AddTransient

 public void ConfigureServices(IServiceCollection services)
    {
        // Strongly typed configuration added to the DI container as IOptions<EnvironmentOptions> etc.
        services.Configure<EnvironmentOptions>(_config.GetSection(EnvironmentOptions.Environment));
        services.Configure<EnvironmentSecretOptions>(_config.GetSection(EnvironmentSecretOptions.EnvironmentSecret));

        // Restore HTTPContext.Current
        services.AddHttpContextAccessor();

        services.AddTransient<IBooksRepository, BooksRepository>();

Finally to return POCO object which are pascal case in C# as native javascript JSON objects with camel case add the [JsonCamelCaseFormatter] attribute to the api controller class.