Oh, dear! I can't imagine that your plan would make it any worse. But it should be sanded to eliminate that ridge, which looks like a tripping hazard. I'd buy another tread to practice on, to make sure the products you're planning on using will make it match better.

Looks like the flooring and the tread is a different type of oak (white oak versus red oak). I would have it match the other treads and be done with it.

@millworkman I really don't want to have to do that since I need to fix his bad feathering job on the existing planks anyway, but it may come to that. Thank you. By the way, it was really hard to identify the oak type. I think it just has a stain over it. Must've looked at a dozen photos on red vs white end grain on the internet... our end grains definitely had features of both, but we're fairly certain it's white oak. Unless some weird hybrid exists! The house is 150 years old, so who knows.