A desktop part will outperform a mobile part for the most part. But it only has to hit 60hz, which the old i5's will demolish. I'm going for minmax there, lowest cost, best results that are in near-parity with the steam box.
They aren't subsidizing the buyer, they're subsidizing the game purchases they get a 30% cut of. (if they were smart, and subsidized it). It also boosts market share by lowering the barrier of entry.
Yes. If not better.
Move up to RX7600 or i5-9500T for a few bucks, or 10500T if you want HT (doesn't benefit games much, especially in the 60hz target of this thing)
MacOS has nearly magical levels of memory compression. 8GB physical ram can store 16GB of actual data, and read and write it at fast speeds (50GB/s) due to having an ASIC dedicated to the compression algo in the CPU.