ng build by itself does not have any optimizations. If you ng build --help you can see all the flags you can pass to further optimize your code and reduce the output sizes.
Try ng build -prod -aot -vc -cc -dop --buildOptimizer and see what your numbers are. This will enable production mode, use AOT, use a vendor chunk for third party libs, pull all common code out into a common chunk, make sure the output path is clean and lastly use the @angular-devkit/build-optimizer for further optimizations.
If that is still large, then do a run through in your application for third-party libraries that you are using. (1) Are you importing the entire RxJS library? (2) Moment with all localizations? etc..
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