You only got 12 million blue crystals for selling all of those. Which is not a fair trade. There's a reason that you don't get a fair trade on most everything, when you sell something in the warehouse, it's for suckas. Selling books for honor badges can be kinda fair, though. But in your defense, if a new player is f2p, probably never have the opportunity to use them. I'm sure someone has done the math but might take ten years to take a hero to breakthrough 30.
Better off selling trash insignia bags from team modes. Especially if you're p2p. And if you're p2p, you'll probably be buying blue crystal bags from the bazaar. And level 9+ insignias. So win-win
Your strategy only works for f2p. But I'm not seeing how f2p could accumulate thousands of apex crystals at the start of the game. Don't think that even exists, at any point. Sorry but this is just bad advice