Really good point and I agree. This was intriguing at first glance because who doesn't want less JS on their site?! Of course! However, missing out on other events being tracked, advanced demographic information(?), and what else?? That's a huge miss - especially if you work with Google Ads and have your Analytics linked. Your ad campaigns won't be as effective and could potentially cost more money to save someone an unknown amount of loading time.

This is pretty creative though.

Wouldn't the 70kb would be most likely already cached too? Which make it even more lightweight than this minimal script.

My firefox never cache anything. Going forth and back in history always reloads the page. That's the reason I have many tabs open - to prevent reloading and waiting.

about.cache says:

Number of entries: 418

Maximum storage size: 30720 KiB

Storage in use: 12698 KiB

Storage disk location: none, only stored in memory

no because expiration of google analytics is really low (30m or 2h i think)

<script async> does still block the document onload event from firing until it's been executed.

What about defer?