Do you think a timer being too short can be a flaw? For example, the timer in New Super Luigi Bros. is a mere 100 seconds and the levels are filled with hazards and platforming gimmicks, but is it now a massocore platformer? If there a reduction in player agency because the levels are now short?
Answer to the first question is, “No duh.”
The key thing with difficulty is, you need to give players some room to breathe. Difficulty is supposed to bring out the depth in a game by constricting and balancing different elements. Too little difficulty and anything is permissable, too much difficulty and everything has to be perfectly optimal. The timer exists in mario to keep people moving along in the level, so they can’t tackle every problem at their leisure, they need to keep up some semblance of a pace. However people dislike harsh time limits as a psychological thing. So when a timer is implemented, it’s better to keep it as something on the backburner, give people enough time that they don’t have to worry about running out as long as they keep moving.
The key aspect with difficulty is balance. All the different elements need to be in a semblance of balance with each other so that the player is pressured to make a selection between them. If the time is too high, players will ignore it like it’s not even there, if the time is too low, then there’s such a hard dropoff point for success that most people will give up. If you give someone too much health, if the lethality is too low, then they’ll just walk through all the enemies and hazards, if you give someone too little health, if the lethality is too high, then nobody is going to work their way up to actually completing anything. These factors are going to work differently based on every game design, every level design.
I have no idea if NSLBU is a masocore platformer or not, though I’d place my bets on not really.
I have no idea what player agency is even supposed to be. It’s like the fuzziest of fuzzy concepts that I hear tossed around, the concept of agency in games. I don’t know whether there’s a reduction in player agency or not because the time limit is short.
What I do know is that only a few players are really willing to stick with a game designed in such a flat way. The Thief reboot had some custom difficulty modifiers that made the difficulty astronomical, but they didn’t really bring out the interest in the game because they made it about executing one specific solution instead of finding a viable solution among many possible ones. Difficulty in a game like Devil May Cry, or Bayonetta, or Ninja Gaiden Black, or God Hand, focus the player to perform better using a variety of tactics available to them. Difficulty in a masocore platformer or a low depth game focus the player to repeat the same few tactics until they work. In Vanquish you try all sorts of different things on god hard difficulty until you come out on top, in Call of Duty, you repeat the same few seconds until you move along or go insane.
The key thing is that without depth, without balance between different competing options, difficulty makes games exercises in frustration instead of interesting problem solving affairs.