Originally Posted by
Yaffy
Popularity is one aspect for sure, but I believe that popularity is mostly an indicator of how easy it is for a player to get a skill combination to a level that they feel like is good, rather than how good the skill is when maxed out. Most people usually settle on a skill set they want to stick with to end game around level 40 or earlier, so most people at end game will play skills that feel good around that level range with some mediocre gear they managed to scrounge up, rather than a skill combination that's good with a full set of max enchanted yellows at level 80 or something along those lines. I know that you have a particular interest in players around that level though so perhaps that's a fine way of looking at it.
That's also partly related to the point you made about skill combinations that aren't very common, but are really strong at end game that are used by a few players. Those builds are unpopular because they probably suck or don't make any sense around mid-level, and only really shine once you have a super good set of gear and the resources to really pump as much into it as possible.
One examples of a skill that's really strong but unpopular as far as I'm aware is Giant bat, which is really hard for newbies to get (Without asking another rare bat player for help at least) and requires books that are only available for a short period of time each year, but then it has some potentially really overtuned abilities like confusing double which are total trash normally but scale ridiculously well with good gear. It seems giant bat is unpopular because it's so hard for a newbie or mid-level player to actually get and then use the skill properly, but it's absurdly good for soloing once you have everything you need to deck it out. I almost never see bat players that aren't around max level, but those that are max level are always doing silly things like soloing bosses.
Another good example is knife which is really easy to acquire, but it's pretty mediocre for newbies because it lacks a lot of utility that make leveling up easier like movement, ranged abilities/AoE (Unless you want to spend lots of money on knives), and good survivability options. I see a lot of newbies picking it up because it's an easily available skill that sounds neat, but I notice a lot of dissatisfaction from beginners with the skill and it seems a lot of those players either quit the game or switch from knife to something else. That said, once you dump tons of money into the skill via throwing knives, venom, whittling, etc it theoretically has really great DPS. It's just that the early game utility is so lackluster and at end game it seems like even high level players don't want to invest in it considering how much it costs to keep it fully powered.
I think one bit of data that could help a lot with balancing skills would be noting how popular skills are at different level ranges, because I think a better indicator that a skill is overpowered would be if a skill is more popular with max level players versus early game players. To me that tells me there are players who are going out of their way to switch off of playing their initial build they went through the game with so they could specifically play a new builds because they thought it was better. Conversely, if a skill is more popular with beginners than end game players, that might indicate that the skill is easy to get at first, but there are problems that make people not want to continue playing it in the long term. Even if the population isn't very big, I feel like there might be some noticeable outliers that could give you insight not just on how to balance skills, but also how to make sure skills stay fun and appealing from the start of the game to the end.