I understand the need to either nerf RC or buff the other two, but this still seems like a confusing way to go about it.
It's not really too confusing, at least not to me. None of the other talents in that tier scale with anything. RC does.
I'm pretty sure you're already aware that I wish they'd just scrap that tier entirely. RE can deliver the most throughput to a certain ability, but it costs your other abilities quite a bit (due to sitting on runes to force the ability you want).
RE suffers when you consider a real human's performance. So does BT, but to a lesser degree, as you can't "waste" a BT-RS like you can waste a RE-RS.
RC beats the other two because there are no restrictions, so it uses all runes without discretion. It's also the most consistent. Entirely worth doing 5% less throughput with DS.
I would presume that DPS classes are still going to take RC. It is the most forgiving, leads to the highest total rune output (compared to gaming RE), and is the most consistent.