She's the main character. Most of anime, no, most of any fiction have the main character ultimately be victorious, except for tragedies, but this isn't clearly one of those. So, no shit she's a chosen one. But just like in any shounen (though this isn't one), she's really going through a lot. Just remind yourself of all the team matches where she didn't seem to have a single easy victory, which quite contradicts how she now could beat two class A's with her left hand (not that these were easy victories either, I reckon). She might be a chosen one, but she has plenty of mental issues.
He admitted himself he's not trying as much as the others. He even gave up karuta once to play tennis. He was never a person who was maniacally driven to rise as high as humanly possible in karuta, no matter the cost. He's a person who puts up a good fight but also admits his own limits and seeks the easy way out. Like any normal Joe. That's why he can't reach the freaks.
That's up to Chihaya and nobody else. If she ever manages to develop a romantic desire and choose a guy. I'm sure both Taichi (well, that's given) and Arata would be highly receptive.