As a daily user of Safari, I can't let you say that. The devtools suck. The network tools suck (why is it so hard to find the request payload??), the elements tools suck, there are basically no extensions (React, Redux, etc.). They are just horrible. As much as I try to use only Safari, I still fallback on Firefox Dev when I need some real devtools.
I use it for the reasons you mention but it's a really bad browser. It's the only browser that still has consistent rendering issues in 2020: sometimes parts of the pages stay blank, CSS grid support has inconsistencies with other browsers, and some basic layouts fail only on Safari.
Another one of my pet peeves with Safari is text selection. It's the worst I have ever seen: https://imgur.com/qC7amU1
It has the potential to be good, but it's just not.