Hi there
I am a bit confused - are you saying that if I have 200 pages indexed in Google, and I have a 40 clicks to my site, that the 5 is an indication of bad SERP performance? Just using your formula:
200 / 40 = 5
I guess that's an okay rule of thumb as you would ideally want every page indexed on your site to be clicked at least once if it's ranked, I just have never heard of that rule.
If you're goal (I am not saying it is) is for every page to be clicked, then yes, 1 or lower would be good because it showed every page is showing up in SERPs. I wouldn't use this as the sole basis of your indexing and SEO performance however, as this doesn't tell you if ALL pages were clicked, or if one page was clicked overall. There's so much more digging you have to do.
Check these resources out: Google Analytics Academy (Google)
Analytics Help (Google)
On-Site SEO (Moz) Moz Academy (Moz)
Local Search Ranking Factors (Moz)
A Technical SEO Guide to Crawling, Indexing, and Ranking (Paddy Moogan)
Internal Linking (Moz)
All of the above will help you way more than the equation you stated above. Again, it's a nice way of thinking about it if you want to just look at those two numbers, but you're not taking into account a LOT of elements. For instance, that number could equate to .01 but that doesn't mean a lot of pages are necessarily getting traffic or appearing in search. The resources I listed will help you better assess your search and organic performance. You'll get so much more out of it and think of things you never thought to track.
Hope this helps you! Let me know if you have any questions or comments! Good luck!