It's a bit naive to think that most websites are referenced by a simple link to static content. The web has become so complex and urls now reflect that. Short urls are useful for many people for many different purposes.

For an example of how complex urls are, take a look at SEO'd blog post or newspaper urls. They have become a string on keyword rich terms that help to increase SEO. The content that is served is brought up dynamically and may in fact change over time. Ads, sidebars, and comments are brought in after the fact, often based on content or origin of the user or if they have a cookie. It's complicated - url redirection (which already may be happening in this flow) doesn't add much to it.

Advocating for "proper link formatting or better content presentation" reflects the fact that you've never had to dig deep into the complex SEO, user, customization, and other general business requirements that arise when running a CMS.

Short urls are valuable because they allow people an ability to simplify the increasingly long urls for use in many different mediums without the worry of breaking or losing portions of the url.

Yes, they often do allow the creator to change them, but that's no different than what any website operator can do natively on their website.

There are problematic situations that can arise, such as when a url shortener goes down. And this has happened, and it hasn't caused any catastrophic problems. It's inconvenient, but it often only affects old content on twitter or facebook. I'm not saying it's ideal, it definitely doesn't add value to the internet. But it's not that bad.

Regarding the 'arcane' input requirements for twitter or facebook. Somehow I think you missed the point of these networks. Twitters 140 characters is part of what defines them. There will always be short message mediums, they are there because people have a desire for short bursts of information. They aren't going away.

I hope that helps to explain why shorteners arose because there was a need, not just to add complexity or more evil to the internet.