Starting permalinks with category–still a bad thing?

For performance reasons, it is not a good idea to start your permalink structure with the category, tag, author, or postname fields. The reason is that these are text fields, and using them at the beginning of your permalink structure it takes more time for WordPress to distinguish your Post URLs from Page URLs (which always use the text “page slug” as the URL), and to compensate, WordPress stores a lot of extra information in its database (so much that sites with lots of Pages have experienced difficulties). So, it is best for the first structure tag to be a numeric one, such as /%year%/%postname%/.

https://codex.www.ads-software.com/Using_Permalinks

I hadn’t heard of this until recently, and was quite shocked. I read some more about it and have found plenty of people stating that it can lead to serious performance issues on large sites.

As I understand this, this only causes a noticeable slowdown if two conditions are met:
1. the permalink structure starts with the category or postname
2. there are a lot of pages. Not posts, pages.

Is this correct? Or does it apply to sites with many posts, even if they have only a few pages? Or has it finally been fixed and is no longer a performance concern?

I thought about changing the way I do site permalinks, but as I started looking at some major sites running on WordPress, I notice almost all of them have blog post URLs that start with the post name or category name. So I wonder: IS this really a serious issue? Is it still an issue? Under what conditions is it an issue?

Thanks!