Yes.

“ Copyright <YEAR> <COPYRIGHT HOLDER>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.”

The copyright assertion is the very first line of the MIT license, and the right to copy the code is granted. Clearly a reasonable person would affirm that that license (and all similar licenses) are based on a premise that code can be copyrighted.

> It is based on the premise that if the proprietary licenses are valid, then also the open source licenses are valid.

>If the proprietary licenses are not valid, then it does not matter that also the open source licenses are not valid.

That’s not true. Imagine a world where proprietary licenses are made invalid.

In such a world a company could take open source code compile it and distribute it (or build a SaaS) without the source code.

Even if you only focus on licenses that don’t prohibit this, most of those licenses require attribution.

So even in a world where propriety licenses were invalid the majority of open source licenses would still have a purpose.

You’re attempting to split hairs to argue on a very subtle technicality, but you’re not even technically right.