alcaray: I don't know what you mean, exactly. But GOG has 3 methods for you to download your purchases: Galaxy, direct download, and the old (unsupported, but works just fine) GOG downloader.
1. Galaxy is a client that tries to be Steam but tries not to offend GOG customers. It will more-or-less automatically keep your games up-to-date and allow you to get game achievements (for games that have them). If you want to use Galaxy, then you have to install the client.
2. You can do a direct browser download by clicking on your game, in your GOG library. Then click on the file you want under "CLASSIC GAME INSTALLERS".
3. You can use the old GOG downloader (my favorite) by clicking the "MORE" dropdown list and selecting "GOG DOWNLOADER LINKS". From there, select the files you want. Before you do, you will have to download and install the GOG downloader client frome here:
https://www.gog.com/downloader OK, that's the download part of your question. As for installation, that is mainly up to the developer. What specifically are you seeing in the installation that you don't want to see?
I can't figure out if you are joking or not.
You think it is ok to hide the classic installers and push the infested with the client installers as the default installers.
I don't see any notice in the download page of the game that says BTW you can also download installers without the client strapped on!
This is clear BS pushing the client. There is no excuse as far as I am concerned. GOG is on a slippery road for a while now, a long while.