I'm assuming they both have more onboard processing capacity and the default controllers don't have the hardware to re-map controls.
Steam input is extremely powerful and does it all in software, though. You can run most non-steam games through Steam, and if it's a game that's also on steam, you should be able to use the Steam app ID to find game specific mappings (though I haven't personally done this).
I bought it, but for a tech company their tech is pretty shit.
On ESPN, if I want to watch 4 games, there are a couple different layout options, and I can pick and add each individual game at my discretion. With YouTubeTV, they have predefined choices of games you can watch. It's not a complete list of combinations, and you don't have layout options (ESPN gives you a one big, 3 small to one side option that's nice). I have two actual TVs where I watch games so the layouts are less of an issue, but I can't put a game on one screen then the other 4 I want to watch on a second screen as background unless I get lucky and it happens to be one of the choices they gave.