That is not really correct, posts are represented differently from threads in Mbin (internally and in the UI). You don’t have to post to a specific magazine / community. If you want your post to just float around in the Fediverse (so have the post associated with just your account + hashtags) you choose the random magazine for the post.
I admit that this is not really intuitive and the random magazine is a crutch for this platform to handle plain posts. To make it a bit easier to grasp I created a PR to select the random magazine if one is not on a magazine page.

But all of what you described is possible with Mbin. As an example I created this post (using the form on the generic microblog page) which you can see under posts on my local account. I would like to add links to federated Mbin and Mastodon instances, but nobody follows me, so remote instances don’t pull posts.

What is currently not possible is to follow hashtags (but you can list posts), but I am going to implement this soon.

What exactly do you mean “to a profile”? Can you give an example of the difference (I never used Mastodon)?

Could you describe your problem in more detail?

Microblogs are always associated to your profile. If you want to post something which is not meant for a specific magazine, the random magazine is what you need to use. It is a pseudo-magazine (and so not federated as a community) which aggregates all microblog posts which are not attached to a real magazine.