Earlier quoted context omitted.
On the downside, it will put all the code into one giant script that has to be downloaded upfront. While a website that loads scripts per page will only load the scripts that are needed on the current page.
Unless your site is made of 4 files/modules, you simply must bundle. ESM will download the files in series, as each dependency is discovered. Then compression doesn’t work as well as it will be per-file. Then of course you can’t tree-shake dependencies from npm, so good luck downloading the whole of lodash on your client. In short you lose the advantages of only download what you need pretty quickly.
I never felt the need to use loadash. But even if a site would do that, it does not seem like a big issue. It is 71k. A Twitter profile page is over 5MB. 70 times the size of that loadash library. An appartment page on AirBnB is over 9MB. An Instagram profile page is over 9MB too.