The current rules for Studious seem somewhat weak and limiting.
Practical Game Dynamics
There are only 3 Mane Characters with Studious. Twilight Sparkle, Faithful Student, Twilight Sparkle, Gala Greeter, and Princess Luna.
Of all the friends – although there are 6 – only 2 are common (Mint Jewelup & Sealed Scroll), the others are either Ultra Rare (Twilight Sparkle, Ursa Vanquisher & Princess Celestia, Ray of Sunshine), Rare (Spring Forward), or Promotional (Twilight Sparkle, Research Student).
If we deal with only one Common card (let's say Mint Jewelup) and with the limit of 3 individual card copy rule, we find ourselves with a scenario where you could have a maximum of 4 cards at one problem with Studious.
In this case it would be pretty bad and likely to break the game. (That's potentially an extra 4 action tokens per turn).
In an absolute worst-case scenario* you could (potentially) have 19 characters (remember, 3 copies of each 6 Studious characters plus the Mane Character) for a whopping total of an extra 19 action tokens per turn. Definitely broken.
But with an average purple deck, within an average game, based upon to availability of these cards, realistically, we might be looking at 2 characters at a problem with Studious at any one time. Winning this faceoff and gaining 2 action tokens would not unbalance the game. In fact, it would very much balance out this power (Studious).
Maybe the wording should change to read an action token per character title or type (some sort of variance of the unique card rule).(ie having 3 Mint Jewelups at a single problem will only yield 1 action token. With an additional Mane Character brings this up to 2).
The wording could read:
Let's look at this variation in an absolute worst-case scenario*.
The main character with all 6 friends with Studious (3 copies of each), totalling 19 characters with Studious. However, there would only be 7 with different Card Titles, totalling an extra 7 action tokens. Although this would be devastating and a game-ender, I don't think this would be unbalanced considering the difficulty (if not impossibility), cost, and effort to get this far with this many characters out, at the same problem, and into play.
Another wording variation could be: