I think Proxima is really going to have her chance to fully shine in the abyss (provided there is no damage cap). It is a slight hassle that she needs to be ramped up every fight, but the amount of damage she is capable of dishing out is well worth the time. She is capable of taking down the final Kang boss in Variant 3 with a single l3, even with the halved attack penalty. He's got ~430k health. I have her as a 5* r4, and admittedly for a long time I just used her for synergies. It's fair to say that her playstyle isn't for everyone, and in some content her ramp up isn't always worth the time. But for future content where health pools are getting higher and higher, her value is going to keep going up. She would decimate a lot of LoL if there wasn't a damage cap of 50k. Tbh I'm really looking forward to what she is capable of in the abyss.
So is it worth ranking Old Man Logan instead of her?
Maybe you should see me playing with her, just saying you might learn a thing or 2...