What makes you say it's not doable on a $300 mobile GPU? There are phones out that cost $300 that have better performance than the Switch.
Also it's really down to the software. They could have targeted 1080p resolution with 60fps with the new Zelda but they would have had to make sacrifices on draw distance, effects, texture resolution, poly count, etc.
That's my point, though. They clearly can't make a game with the features of BotW - draw distance, effects, etc without major compromises.
Not personally aware of any games as full-formed as BotW that are running on $300 mobile sets. Though this could just be poorly optimized, which makes it more disappointing.
I don't think anyone has cracked making an open world game on a phone. But just from raw hardware specs perspective there are phones with more performance than the Switch.
