I do have input, but not on the Cubecraft thing. Not a huge fan of Minecraft to begin with, so I’d never spend money on it.
I feel I should explain something, shed a bit of light on your son’s PoV because for years my parents did the same thing you do.
This is what I’m talking about.
For YEARS, my parent bought games for me, thinking they always knew what games I liked, when ultimately 90% got finished and never touched again, and they only got finished because I felt bad telling my parents that I didn’t like it, when they really tried to be nice and put effort into getting stuff for me. This only really stopped when I turned 17 and decided it was time to tell them. I felt so bad, though.
I think this may be a case of the same thing, except he finds his joy in this one game, and I can’t say I blame him. I’ve come across F2Ps that had me going for a long time and I have spent quite a sum of money on them (like fucking Warframe. I have spent a few hundred on that, maybe $400?). In the end, it’s not a whole lot different than buying another game. It’s unlocking content, privileges, and things you couldn’t otherwise do, except it’s on something you definitely enjoy, and will continue to enjoy for a long time to come. In such a case, what’s wrong with supporting it?
Also, it’s better than most stuff of similar origin that have a monthly cost or some kind of regular subscription/repurchase. It’s only one buy that he’ll have to make, as opposed to an ongoing thing. Much better in the long run because he enjoys it, and it’s not 100% pointless.
I won’t pretend to know how you feel on the subject or tell you the best course of action, but I do have an idea of how he feels, even with the limited information I’ve been given. I won’t say “let him do what he wants”, but I can safely say in this particular instance, that a single expensive purchase is FAR better than successive purchases that are usually equally expensive for something he might not enjoy nearly as much.