Is ripping off an open source library okay?
Yes, absolutely. Copying an open source library, even if you make no changes, or only make trivial changes, is completely OK as long you follow the requirements of that library's license.
In the example you have highlighted (SAConfettiView vs. SwiftConfettiView), the author of the fork (SwiftConfettiView) has apparently not followed the license requirements of the original (SAConfettiView), because he has not retained the copyright notices as required by the MIT license. See @apsillers answer for further details about this.
However, in general, copying a library, even if you copy it verbatim or make only trivial changes, is generally allowed by open source licenses, including the MIT license. In general, none of the things you complained about is actually a problem. Let's look at each of your complaints:
No credits given to the original author or project.
Open source licenses, and the MIT license in particular, do not specifically require "credits" to be given to the original project. For example, if your app features a "credits" screen of some sort, the MIT license does not require you to place any particular notice there. If your app does not feature a "credits" screen, the MIT license does not require that you add such a screen. The MIT license only requires that you retain the required copyright notice(s).
The guy just renamed the project and literally took ownership of it, and just updated some little codes.
You are not required to change a certain amount of an open source project in order to distribute your version. If you want to copy a project verbatim, that is allowed. If you want to copy a project and make trivial, meaningless changes to the source code, that is allowed. If you want to copy a project and introduce subtle bugs here and there, that is also allowed.
If you think about it for a moment, there is really no need to make any requirements on what changes you make to an open source project. If the new version actually is better than the original, then people will eventually use the new version in favour of the old. On the other hand, if the new version is simply a copy/paste of the original, or if it introduces bugs or is generally worse than the original, there will be no reason for people to use the new version, so they will just continue to use the old version anyway, and the new version (the "rip off") will eventually be forgotten. In any case, the original author is always allowed to incorporate positive changes back into his version, at his discretion.
Didn't bother to just fork the original project.
In general a "fork" just means it is a copy of the original, with or without changes. In GitHub, there is also a "fork" button that you can use on a GitHub-hosted project which copies that project and links it back to the original, but if the project is released under an open source license, there is never a requirement that you use that particular button in order to release your own version of a project.