FWIW I still disagree with your disagreement
300MB for tmp is usually more than enough and, I think, is an acceptable default for a separate partition setup - having a default size of (for example) 4+ GB for a partition that in most cases will hold < 100MB of data would, IMHO, be a bug ...
As well as the prompt in the partitioning step to choose "all in one" if you're unsure, it's also covered in the install documentation (which you read, right?
)https://www.debian.org/releases/stable/ ... -partition
https://www.debian.org/releases/stable/amd64/apcs02.html.en wrote:/tmp: temporary data created by programs will most likely go in this directory. 40–100MB should usually be enough. Some applications — including archive manipulators, CD/DVD authoring tools, and multimedia software — may use /tmp to temporarily store image files. If you plan to use such applications, you should adjust the space available in /tmp accordingly
Debian provides a lot more than your average "cool desktop focussed derivative distro" aimed at casual users, and consequently requires a bit more thought about what you want.