Make card droprates more consistent

This has been prompted by an experience I had today grinding cards, but I think is reasonable in the wider scheme of things.

I was in the map Camp 3 trying to farm Officer Skeleton cards. According to the library, there are 14 officer skeletons and 6 skeleton soldiers on this map (although in practice, there looks to be a lot more of both). Despite this, I had 10 drops of skeleton soldier cards in the time it took me to farm 5 officer skeleton cards. I recall something similar happening on my bowmaster and my shadower when I farmed these cards on them, although I don't have specific numbers to back this up.

If we assume I got average luck here (which I appreciate is quite an assumption), that would mean that the drop rate for skeleton soldier cards is around 4.6 times the drop rate of officer skeleton cards. Even if I had horrible luck on the officers and the expected rate would be to get 5 of both cards at a similar speed in this map... that still puts skeleton warrior at over 2 times the drop rate of officer skeleton.

The question I have, then, is "why?"
What benefit is there to the drop rates being so wildly different from each other?

I could understand if it was balanced with something else in mind, like the values of items dropped, or the exp gained, or even just how popular the maps were to grind at before the monster book was implemented, but both of these mobs should be pretty similar in all of those ways and I fail to see a pattern like this in the wider scheme of things. It just seems random. If there is a pattern and I've just missed it, I'd love to hear what it is

To be clear, I'm not saying to make all of the card drop rates exactly the same. What I am saying is: reduce the drop rates on cards like pinboom that take 5 minutes for the full set and increase drop rates on anything that's super low (like Officer Skeleton seems to be). Would it not be more balanced and more fair to players to normalise these drops rates?