Exactly. It's harder than it sounds to ask the right "why".
Search-Lemmy is under development for this.
Not really. Also by your logic you can't trust anyone ever because there is always a risk they turn bad at some point in the future. All we can do is evaluate what we have in front of us at the moment. Current evidence suggests Ruud is trustworthy, committed and capable of running a large Fediverse instance.
Well Ruud who runs .world also runs Mastodon.world which is a fairly large mastodon instance, so he is somewhat of a known quantity and has experience running large Fediverse servers. His mastodon server has handled a large population and donations happen through Open Collective for transparency as well. He also runs Calckey.world though that is much smaller.
The danger in randomizing servers is that some smaller servers not only have less than 99% uptime but are also just run by random regular people who couldn't handle the increased load and/or have no desire or ability to keep the servers running long term. It could maybe work if the randomization occurs from within a vetted list.
Account migration is a feature that has been noted for the future and would indeed be very important since it would essentially make the entire network bulletproof. Being able to move instances and/or link accounts across multiple instances would create the necessary redundancy and reduce fears of choosing a smaller instance as home.
The idea of combining the two isn't necessarily bad, Kbin has some good ideas and I guess that's why it's gotten popular, there are just some baffling stuff too.
The leftover terminology from Mastodon makes some sense (haven't used that one myself), maybe the founder thought the majority of users would join from there, but the magazine thing just confuses me since they are clearly just communities filled with threads. When I browse single picture meme posts or questions on AskKbin my first thought isn't "ah yes, Articles in a Magazine".
In addition to the backend, I'm not sold on the terminology used in the front end either, though visually it does look good.
Why call communities Magazines? Why am I starting a microblog when I press new Post? Why is upvote called Favorite and what does Reduce mean? And what the hell is Boost and how is it different from Favorite?
Still, the number one issue at the moment for sure is the slow federation and syncing with Lemmy. Communicating across different Lemmy instances is no problem, but Kbin<->Lemmy seems incredibly slow, with threads from Lemmy often lagging many hours behind when viewed from Kbin which makes it impossible to participate in conversations.
A lot of UX work still needs to be done for sure. Not sure if it's exactly what you're looking for, but there are scripts to redirect links to your home instance if that's what you mean. Try these (requires a userscript extension like Violentmonkey):
I'm waiting for both Sync and Boost to come out with their Lemmy offerings and will probably end up with one of those. In the meantime, I'm trying Thunder and WefWef, but have also heard good things about Liftoff. Here is a list of the current (and upcoming) crop if you want to experiment: https://lemmy.world/post/465785