It is true that the KaOS community is quite small, so it will happen that you have to wait some hours before a response in the forum (I for example do have a job too and do not sit at the computer/forum all day to answer any and all questions right away). But what is behind in KDE? All frameworks, Plasma & KDE apps are the very latest. Plasma 5.14.90 is available for testing (https://forum.kaosx.us/d/2283-plasma-5-15-beta-up-in-kde-next).
The very latest is available of Qt (5.12.0), latest kernel (linux-next 4.20.4), glib2, gtk3, just a very large rebuild done for latest python 3.7 and so on.
So no idea what you are complaining about there with
Calligra stage is upstream marked as unmaintaiend, has had no commits or fixes to speak of for over 2 years, so it is not included in KaOS builds (default Calligra build). If you know of something new regarding stage and it is maintained again, than of course it will be included again. (are you sure about that kind of money going to calligra? for the last 3-4 years, only one dev is working on plan, and has that split off from calligra now too, just like kexi & krita, the rest of calligra is basically dead, one KaOS users is the lone somewhat active in karbon).
As for applications missing, that is by design, every users will see 5-10 of what they find as essential missing, multiply that by say one thousand users, and the repo needs to grow to 8000-10000. The design is to keep at the current maximum of 2100 packages. And you are right, that is not enough for many, but that is also a choice from the start (already 6 years ago, no change whatsoever in all those years regarding the goals or size.
All that is spelled out in the website though:
And as for what you find missing/complete essential for your needs:
KaOS vs responsiveness of Fedora 28 KDE
I presume you mean Fedora is much better? Or KaOS more responsive? KaOS for all regular users is faster than any other KDE, that is why they stick around, so I'd like to see some logs/error messages as to what is going on with your system. But of course understand too if you have decided that KaOS is not for you and moved on to a distribution much better suited to your needs, thus no logs will be available.