What if I release my own SaaS as AGPLv3? Do others, who rely on it, also have to license their software under AGPLv3? I think this kills many business cases.
Am I missing some key point?
If you link to it directly from your code then yes, unless you're willing to pay Grafana for a commercial license (assuming they offer one or you can negotiate one with them). If you have Grafana running on your servers but you aren't using the code in your own applications then you're generally fine (the GPL is generally recognized as ending where a process ends). And that's the point of the GPL/AGPL, you get the code for free, with the only expectation being that you pass it on if you make any changes.
You wouldn't, as system interfaces are specifically excluded as an AGPL enforcement domain. But if the Linux kernel was AGPL, you would have to supply the source code to your NFS clients, since those clients would be served directly by the kernel.
More specifically, the only difference between GPL and AGPL is section 13 (and the preamble summary). The rest of the license is word-for-word identical (save for the name). https://www.gnu.org/licenses/agpl-3.0.en.html#section13
I'm sure if I'm wrong I will find out very quickly, this is HN after all.