10 MB could be an exaggeration on average, but not by a huge amount. Not even trying to find something crazy big, this is the first site I checked because I went to it earlier today and noticed it took a long time to load:
https://help.salesforce.com/articleView?id=000232181&languag...
It is simple help article, but instead of serving the actual help article it spends about 2 seconds serving 4 MB of JS and rendering the article.
After that I typed 'app.' into my URL bar and went to the first site that came up, that was 3.9 MB of JS on the login page.
Numbers are for uncompressed JS, including the larger of the inline scripts.