ToME: the Tales of Maj'Eyal

I am currently playing a Solipsist on Insane difficulty. I was trying to decide how to invest my skill points, and after doing a bit of mental math it seemed to me that Psychometry was my best bet - I was wearing 12 pieces of natural/psionic/antimagic gear, each with a material level of 4 or higher. Raising Psychometry to rank 4 should, according to the tooltip, grant me min(2.0,4 * 50%) = 2.0 mindpower per piece, for a total of 24 mindpower.

Upon investing the 4 talent points and looking my character sheet, I was disappointed to find that instead I had received a grand total of 3 mindpower.

I was going to file this as a bug, but first I decided to read the source code and run a couple test in the in-game LUA console, and what I found was that this appears to be intentional behavior. player.attr:("psychometry_power") was being correctly calculated exactly as I expected, but added to the total mindpower value *before* diminishing returns are calculated. This results in a total return on investment of less than a single point of mindpower per talent point in Psychometry, which seems... questionable.

Now, on Normal or Nightmare difficulty, this might not be that big of a deal, but at level 40 on Insane I am starting to regularly fight non-psionic enemies with mental saves that are a full tier above my mindpower. 24 points of mindpower would have made a substantial difference, but 3 isn't even worthy of consideration. Diminishing returns make it incredibly difficult to accurately gauge which talents will benefit me the most, and some talents wind up being completely worthless to invest in because of it.

I feel like ALL talents that grant saves or power should include in their description the adjusted value that the player will receive, and honestly the rules surrounding diminishing returns might need to be revisited as well. Perhaps bonuses from talents should not be subject to diminishing returns, but bonuses from equipment should?

The scaling on power and saves is intentional.

Mindpower, Spellpower, etc. are the basis of raw damage for many abilities and the scaling takes into account other enhancements (mostly multiplicative) for this damage from equipment and other talents. As a general rule, you need to advance 2 (sometimes 3) sources of damage enhancement for a skill as you level to keep up with tactical demands. Without diminishing returns on various bonuses, scaling would quickly get out of control (and often did in earlier versions of ToME), and play on higher difficulties would become essentially impossible.

The other thing to take into account is that the game is primary balanced around normal difficulty and not all class/talent combinations are equally viable on higher difficulties. For example, talents that allow the target a save to negate their effects become far less useful against NPC's that are much higher level than the player.

Clarifying the difference between raw power/saves and their adjusted values (in tooltips and ability descriptions) is a good idea and is being slowly implemented in the game.

the thing is that this talent, becomes completely useless later.
when you compare like a weapon mastery of sorts, you get both Ppower to carry you early, as well as % increase to keep it useful later. this talent however, not only give far less Mpower overall, but also the bonus shrinks dramatically as the game progresses.

same goes for the archmage's arcane power talent. it gives 20 to 25 raw Spower, at a cost of 5 points and mana sustain.