We use dwarfs in order to provide more features to the users instead of maintaining the status-quo. Even if most of the games are small, at a high scale of quantity the mounting system will be useful to people that want to seed them. There are other various advantages such as overriding game files instead of overwriting them for example when mods are used that way.
The reliance on up to date systems is mainly because outdated ones can yield different results than what was tested. We also use the new wine vulkan mechanic from wine and plan to replace dxvk with it as much as possible. This makes the scripts more reliable instead of requiring to reach github for the latest dxvk version.
We dont want to pack any of this open source software with the game files given that they receive updates and it would take away the convenience for the user to use its own compilations and so on.
Latest wine is of course available on stable distros as well.