I think we're quite off topic from your original question, which has been thoroughly answered: There is no mechanism (by design), in 4.5, in which you can extract purchases from Marketplace and then install them elsewhere without using Marketplace. This is not a function of planned obsolescence, but rather an effort to streamline the experience of purchasing and installing addons for those community administrators that cannot or do not wish to manage code, and to make lives easier from a customer support standpoint. Does this tradeoff come with the issues you've mentioned and more? Yes. Is this good for all communities? Absolutely not.
You can tie an internet accessible "test install" license to Marketplace and your production URL to Marketplace and install and upgrade purchases from there, or install things you or others make via the manual upload option.
If being able to download and upload code outside of the Marketplace is important to you, for whatever reason, don't buy things from Marketplace. Write and maintain the code yourself, or work with developers directly and off the Marketplace. Pay attention to license terms. Just because you can technically do something doesn't mean it's okay to do so. Just because you have a copy of software in your possession does not mean you can install it wherever and however often you'd like to. You purchase a license to use the software; you do not own it.
As a matter of best practices, I'd highly discourage running any code that is no longer maintained for security updates. There have been major security issues in every product you've mentioned, and many of them are end of life and no longer being maintained.
Good luck!