Ajax path to add item to cart (routing override not working)

I'm trying to override the below ajax path to add an item to the shopping cart from within a plugin that I'm setting up:
addproducttocart/catalog/{productId}/{shoppingCartTypeId}/{quantity}
Since it's not working, I'm wondering if this is even allowed? The normal code takes the ajax path above and re-routes to the Shopping Cart controller's AddProductToCart_Catalog ActionResult method.

I created my own shopping cart controller with a new method AddProductToCart_Catalog ONLY within my own namespace, and the re-routing isn't working. When I call the ajax function with the path w/ajax, it still goes to the nop.web core version of AddProductToCart_Catalog  ActionResult (I added a breakpoint in the shopping cart controller there to check and it still gets hit.) (Am I missing something?) (Do I also have to override the AddProductToCart_Catalog method in the shopping cart controller as well?)

Here's my routeprovider code:

using System.Web.Mvc;
using System.Web.Routing;
using Nop.Web.Framework.Localization;
using Nop.Web.Framework.Mvc.Routes;

namespace Nop.Plugin.Custom.DealerDoorSelectionCenters
{
    public partial class RouteProvider : IRouteProvider
    {
        public void RegisterRoutes(RouteCollection routes)
        {
            routes.MapLocalizedRoute("Plugin.Custom.DealerDoorSelectionCenters.AddProductToCart-Catalog",   
                            "addproducttocart/catalog/{productId}/{shoppingCartTypeId}/{quantity}",
                            new { controller = "ShoppingCart", action = "AddProductToCart_Catalog" },
                            new { productId = @"\d+", shoppingCartTypeId = @"\d+", quantity = @"\d+" },
                            new[] { "Nop.Plugin.Custom.DealerDoorSelectionCenters.Controllers" });

            // Original local route here:
            //routes.MapLocalizedRoute("AddProductToCart-Catalog",
            //                "addproducttocart/catalog/{productId}/{shoppingCartTypeId}/{quantity}",
            //                new { controller = "ShoppingCart", action = "AddProductToCart_Catalog" },
            //                new { productId = @"\d+", shoppingCartTypeId = @"\d+", quantity = @"\d+" },
            //                new[] { "Nop.Web.Controllers" });

        }

        public int Priority => 10;
    }
}