If a webserver were to use this license it would still allow most enterprises to use it as a web server (IIUC) except if you are offering an open proxy service.
All websites and even value-add proxies likely would not be impacted
I think you're underestimating the impact that the webhosting industry had on the popularity of Apache httpd, all of these related ecosystem projects like PHP, MySQL, etc., and even Linux itself. How many small businesses launched because cheap and good webhosting was plentiful? How many developers cut their teeth making web apps that worked on the average cPanel/WHM webhosting provider? The answer to both of these is "A lot. A whole lot."
I did not think of this, if I understand the license correctly an AGPL webserver used to host third-party websites would only require the ability to download the source of the webserver, while a whit SSPL it would require the ability to download the source for both the infrastructure and the hosted application.
Definitely a different tradeoff that many would not have been confortable in choosing.
All websites and even value-add proxies likely would not be impacted