This is just how any monetary-based system works, and it's also a big part of what differentiates Splinterlands from a traditional game. We cannot both allow the cards to be transferable / sellable and give them away for free. That would be exploited in short order and kill the game as we have seen with a number of other blockchain-based games that don't get this concept.
So yes, any game with transferable / real-valued assets will necessarily be a money game. Do people complain that every time magic the gathering releases a new set of cards you need to spend a bunch of money to purchase them to remain competitive?
We realize this type of game is not for everyone, and that's fine! There are thousands of great games available where you can progress without spending much money, and many of them are much better than Splinterlands right now. But of course they are strictly games and don't offer the financial / collectible elements that blockchain-based or physical games do.
I look at Splinterlands (as well as most blockchain based games) as a combination of an investment vehicle and a game. You can invest in Bitcoin, for example, and you just watch the price and see if it goes up. Similarly you can invest in Splinterlands cards, but you can also have fun with that investment, and earn a return on it by winning more cards/DEC/etc through playing.
But you cannot earn a return on your investment if you haven't made an investment. And obviously the larger your investment, the higher the return you can earn will be.
Regarding your son, here's how i think about this with my son which i think is really cool (and please do not take this as financial advice). I try to save up money for my son (for college or whatever) but i also want to spend money to play games. What's so cool about these types of games is that they can potentially allow me to do both together. I have no idea how this will work out, and i certainly don't put all my money into this, but when i buy assets in a blockchain-based game i look at it as both an investment into my future and spending money in a game.
This is something that generally did not exist before, and is really exciting to me.