First of all, I think that your developer should do his own research into how Webflow works. From these questions it is clear that he hasn’t done so much as a Google search…
This is a community forum where Webflow enthusiasts help others with their problems for free, so for specific questions I would contact Webflow directly. However I will answer as best I can.
Does he mean high availability? The site you build with Webflow is just a bunch of static assets that are served from their CDN. I believe they use Fastly behind the scenes. If that’s not highly available enough then don’t use Webflow for hosting. You can always export your code and host your site anywhere else.
If he means the performance cap of the websites that Webflow creates, then I guess this performance cap would be the same performace cap that Fastly has.
Does he mean DDoS? If so then again this would be whatever Fastly has in place. They document this here.
I don’t understand this statement but I will take a guess that he means version control? If so then he’s correct about that. Webflow has no real version control or branching. There are automatic backups but of course this is not akin to proper git branching. IMO this is a major issue, but I dare say that the majority of Webflow users don’t come from a software background and don’t know what they are missing. I highly doubt Webflow will ever address this.
Webflow is fine if you only use it for its intended purpose - static marketing, brochure type websites. Countless businesses rely on Webflow so I disagree with the statement that it’s not production ready. You just need to be aware of its limitations (which are well documented in this post).