2015 and 2016 rank up gems and gold

To the mods, just some feedback on variant rankup gems.
First, I’m curious as to why the 2015 gems do not cost gold but 2016 do. Is there a reason or intent behind that?
To that point, I haven’t used a single 2016 rank up gem, for the sole reason that I have to be extra prudent in management of gold as a resource.
I have a few I’d like to use them on but unfortunately I cannot. I have to prioritize gold spending on champs that will actually be viable for finishing act 6 story content.
First, I’m curious as to why the 2015 gems do not cost gold but 2016 do. Is there a reason or intent behind that?
To that point, I haven’t used a single 2016 rank up gem, for the sole reason that I have to be extra prudent in management of gold as a resource.
I have a few I’d like to use them on but unfortunately I cannot. I have to prioritize gold spending on champs that will actually be viable for finishing act 6 story content.
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I also have two skill. I guess I’d use one on crossbones. And the other sheesh idk. Unfortunately BPCW would probably be the second best option which isn’t saying much. But how could I bring myself to spend 500k gold to R4 BPCW?!