Excellent comments, thanks!
The crafting definitely needs some work. Overall, it's a bit too cumbersome—too many items, too many recipes, too complex crafting chains—and it definitely needs to be either simplified or the crafting system itself made more user-friendly.
I also agree about the slow progression. During a normal playthrough, there's a constant mana shortage, which is annoying. During development, I was more focused on coming up with mechanics and features in general and how they interact with each other. I spent less time on balance and progression. These things won't be difficult to fix.
I was planning to add more automation and idle elements to the gameplay—increasing minion auto-damage, auto-combat with spheres, auto-completion of raids, etc. I also have ideas for an Expeditions mode, where you'll send groups of minions on independent expeditions.
The final levels of minion upgrades, requiring thousands of cores, are simply placeholders until all evolution stages are fully designed. And for the final three bosses, the key was in the sequence and opening new damage element type. First, upgrade the Bird minion (Never-Echo-Omen) to stage 3 and gain Blood damage to break the Chaos shield of the Zalthor sphere. Then, as a reward, get the next minion with Chaos damage to kill the next sphere with Fel Shield, and so on.
I think it would be a good idea to design a Tutorial system to indicate upcoming tasks and milestones for the player to complete (something like a Quest Journal). But first, i need to catch a bunch of bugs and fix everything, to make people stop hating the game :D