That's also my biggest gripe with the Touch Bar so far; that you cannot disable the aggressive 60-seconds dimming behavior. I'd like to have it on at all times, or at least have a significantly longer timer before it starts dimming.
You can try creating and running an AppleScript that regularly "taps" a key as described
here in order to keep the TB awake. However, for me on a 2018 MacBook Pro, this won't work; from all I can say, it needs to be an actual physical input that keeps the TB awake, a software-sided keystroke from AppleScript won't do it. Since the comments over there indicate that it does work for some people, I can only imagine that either High Sierra or the 2018 MacBook Pros made some change about this dimming behavior and made it so that only inputs on the actual hardware will turn it on. If you have a MBP from before 2018 then it's possible that this method will work for you; otherwise probably not.
It baffles me that there is no option at all for this when a simple slider, just like the one for how long the display itself stays on without input, should be very easy to implement for Apple. The only reason I can think of is to counteract burn-in, but that doesn't stop Apple on the Apple Watches or newest iPhones from providing an option for how long the screen stays on either (and it's not like burn-in is much of a problem with Apple's OLED screens to begin with).
I support OP's request: if anyone has a workaround to prevent the Touch Bar from dimming, it would be greatly appreciated. Maybe is a hidden terminal command or something that I could not find.