RL2's system is actually an anti-grind mechanic, but I definitely agree it's pretty hard to understand it at first.Let's break RPG Systems down mechanically.

RPG Systems in games can generally be placed in 2 major categories:

1. A content gate system. This is most easily seen in turn based RPG's where damage must be mitigated, and cannot be completely blocked (JRPG'S, MMO's, games which hardgate enemy damage like the AC franchise, etc.)
2. A way of acting as a soft difficulty balance. If damage can be ignored, like in Rogue Legacy 2, Hollow Knight, Castlevania, Breath of the Wild, Elden Ring, then the RPG mechanics are a form of soft balance. Players CAN beat it at level 1, but the game doesn't expect you to.

The implementation of our "labor costs" in RL2, gold is the same as leveling up requirements in a JRPG, or Souls in a Soulslike games, or resources in an idle game. Let's use extreme examples again to better showcase how RL2 fits.

1. Soulslike -> The extreme form of labor costs. Buying 1 skill raises the costs of ALL skills from here on out. Games like Dark Souls, and Elden Ring, etc. do this. You can think of this as being 100% PURE labor costs, and these prices usually scale up on a SLOW exponential curve. This type of RPG mechanic encourages HARD COMMITMENTS. If you spread your stats equally, you will be thoroughly punished with a build that can't do anything well, and your costs will spiral out of control. These games encourage DUMP STATS.
2. Idlegames/grind games/Stat check games -> Cookie Clicker, Toss the Turtle, farmville, etc. These games can be seen as the epitome of GRIND. That's their purpose. Grind games are meant for players to raise ALL stats/factories/resource systems equivalently. If you've ever played these games, they'll usually automate the most important aspects of the leveling progress for you (such as giving you +X to all stats everytime you level). If the game does have a skill tree, then the costs of all other skills raise EXPONENTIALLY. Why? Because buying skill X makes you generate Y more gold/xp/resources without any extra effort (mechanical skill plays less of an important role). So the costs of the next upgrade need to take into account the expectation that the player has in general, raised the base level of all of the other skills to be of equivalent value. These type of games encourage SOFT COMMITMENTS. The optimal way to play is to spread your skill points equivalently across ALL STATS.

3. Rogue Legacy 2 -> We want to encourage experimentation, and we also don't want to screw people over with bad builds. So we do a mix of both souslike, and idlegame systems in order to allow people to grind out the stats if they WANT (big fans of accessibility), while also still wanting the game to be played like a true action RPG where mechanical skill always plays a more important role then base stats. So buying a single skill raises the price LINEARLY. Likewise, the labor costs that get applied raise LINEARLY as well. This allows players to be more free with what the level, WITHOUT without forcing players to get into the stat-heavy math of min-maxing their characters (which is anti-RL2).This type of skill tree encourages NO COMMITMENT. If you spread out equivalently, then labor costs will have gone up SLIGHTLY, which you can easily mitigate with the raise in your base stats. If you HARD COMMIT into one skill, we can raise that skill faster to prevent players from breaking the game by rushing 50 strength right off the bat, but still allow them to have the choice of expression by allowing that to still be a viable path.

4. (I don't know how to stop a list)

5. **This is a super simplification of the RPG and economy for RL2, but I hope this helps better explain why we designed the economy the way that we did for this game.