Since "approving" can be done with both voting and boosting, I feel like the context of the vote is different. It's more like something I'd want to see implemented as "drag and drop the posts to help rank them". You would still have people who try to bury things by moving them to the bottom of the thread, but the additional friction of ranking high-to-low would turn the reaction into a more complex "but which one of these is actually the Best Comment". Like, you'd automatically bias towards putting the best at the top, not burying the worst.