Alias is maybe better?

app/frontend/styles/application.scss

@@ -10,8 +10,8 @@ $govuk-font-url-function: frontend-font-url;
 $govuk-image-url-function: frontend-image-url;
 $govuk-global-styles: true;
 
-@import "node_modules/govuk-frontend/govuk/all";
+@import "govuk-frontend-styles";
-@import "node_modules/govuk-prototype-components/x-govuk/all";
+@import "govuk-prototype-styles";
 
 @import "accessible-autocomplete";
 @import "button";

webpack.config.js

@@ -43,6 +43,10 @@ module.exports = {
     ],
   },
   resolve: {
+    alias: {
+      'govuk-frontend-styles': path.resolve(__dirname, 'node_modules/govuk-frontend/govuk/all.scss'),
+      'govuk-prototype-styles': path.resolve(__dirname, 'node_modules/govuk-prototype-components/x-govuk/all.scss')
+    },
     modules: ['node_modules', 'node_modules/govuk-frontend/govuk']
   },
   output: {