You're not wrong in that a van makes far fewer trips than individual cars do. This is one thing I didn't research. I just started reading about it thanks to your comment and, as with everything, it's a complex issue. Amazon's pivot to 1-day shipping has the potential to negate the benefits of package delivery versus driving to the store, per this piece in Vox:

https://www.vox.com/the-goods/2019/10/16/20917467/amazon-one-day-shipping-bad-for-environment

I plan to research this more - thanks for bringing it to my attention..

Stopping my dependency on Amazon is part of a larger move to change my behavior about consumerism (fodder for another piece). For example, by better planning trips for supplies, I want to reduce my trips to the store to once or twice per month. I'm also trying to buy less and in more sustainable ways (thrifting). 30 orders a month for one household seems excessive, particularly when considering the packaging. I wonder if this is a superuser mentality and how many people routinely do this.