That's good to hear! I figured there wouldn't be any point in them insisting on keeping the branding anyway, but it's always good to make sure.
In regard to Big Picture Mode, that is exactly how that works - the controller simulates keypresses that are defined in the preset. It has nothing to do with the Steam Input API, which you would normally use to integrate controller support.
The documentation you're looking for is here:
More specifically, there's also this section under "getting started for Devs": [LINK], where the stuff that probably applies to you is under "Selecting a configuration for my non-Steam Input API Game"
In regard to Big Picture Mode, that is exactly how that works - the controller simulates keypresses that are defined in the preset. It has nothing to do with the Steam Input API, which you would normally use to integrate controller support.
The documentation you're looking for is here:
[LINK]
More specifically, there's also this section under "getting started for Devs": [LINK], where the stuff that probably applies to you is under "Selecting a configuration for my non-Steam Input API Game"
I hope this helps a bit!