Firstly, thank you so much for feedback! There's a lot there, so I do actually want to respond and share my thinking and maybe I can learn a little bit on refining my own process.
Secondly, I wouldn't really consider this a game meant for "casual" players. I wouldn't conflate cozy with casual to be more specific. I think there's absolutely a market of people who play MMORPG's daily, but are less interested in heavy combat mechanics and would be more interested in the social, collecting, and other systems on offer.
Thirdly, to address the complexity of systems, I would agree simpler is better! The complexity of the currency system is a little deceptive; the complexity is given as a method for developer side to combat the inevitable problems of inflation that simply exist in MMO's. It is a little complex, but it's not mostly player facing so my hope would be that the complexity of the solution is only as high as the complexity of the issue it seeks to address.
As for the breeder's shop, the male pet thing is an arbitrary decision on my part. For some reason, it made sense to me because I was considering how people in agriculture tend to address breeding related transactions, but this isn't really necessary in a game, so that is a really excellent point.
I would consider "Fabled" to be a disposition that would make other parts of the game irrelevant if it could be 100% passed down, so my first instinct is to err on the side of caution, and make it nontransmissible. These are the types of animals that could be earned as a reward and could be something players want to invest a lot into, but I want it to feel magical and rare. I would say the bigger issue is that having a "Fabled" pet would make someone significantly more likely to win competitions more of the time, and...I haven't considered yet how to combat that, but that's a glaring design error.
If breeding and the marketplace are the systems you feel obfuscate the premise of the game, I would like to hear more about that. What do you feel, looking at this GDD, is the experience you would be hoping to have, and how do these systems keep you from having that experience specifically?
Again, thank you for the feedback, I would really enjoy a chance to hear more of the specific issues you have with these systems as a player. These insights are worth more than Gold (pun intended).