Ok, but what does “genius-level intelligence” mean? This doesn’t actually tell me any more about what kind of roleplaying is expected of the character than the number 18 does. I still, as a player, have to guess at what you think is appropriate roleplaying for my intelligence score and hope you don’t decide I’m acting “too smart.”
Ok, so this is actually another double-standard. If you think my character is “smarter” than I am based on their intelligence score, I’m allowed to rely on the results of dice rolls to express the difference. But if you think I’m “smarter” than my character is based on their intelligence score, I have to play “guess how the DM wants you to act” or be labeled a dirty power gamer.
This, in my view, is one of the problems caused by assigning DCs to tasks independently of an actual attempt to perform them. You’ve decided that this puzzle requires a DC [X] intelligence (Investigation) check to solve, and so a character whose bonus to Intelligence (Investigation) is less than [X-20] objectively can’t solve it if a roll is called for, which makes it feel like cheating if you allow them to solve it without a roll, based on their stated goal and approach. On the other hand, if you only assign DCs to active attempts to complete tasks after they have been announced and you have determined based on the stated goal and approach that a roll should be used to resolve them, this problem no longer exists. There are no tasks that a character can’t succeed at with a roll because you don’t call for rolls if the character can’t succeed.
Which is all well and good. If it works for you and the folks you play with, by all means, do whatever is fun for you. I’m just explaining the issues I personally take with this style and why I prefer to run things differently.
Let's say you're a clever player in my game. You come up with good ideas/plans, remember details, connect the dots in plots, etc. I have no way of
knowing just how smart you are, but the way you play works well for a PC with above average INT. If you, as a player, fail to think of something, but your INT 18 PC probably would, I'll let you roll and either give you a hint or just have your PC "think of whatever".
But, let's say you're playing an INT 8 PC. Now, because of how smart you are you routinely take charge, plan assaults/tactics, etc., things that repeatedly would be difficult for someone of average intelligence, let alone lower intelligence. What you are doing is giving yourself a dump stat where (due to other choices you make)
really has no significant negative impact on your PC. Because you play your PC smarter than they really are, role-playing-wise you have all the benefits of a high INT PC without the high INT.
I have seen this sort of thing often enough after playing for over 40 years. Fighters with INT 6-8 come up with
brilliant tactics, solve complex puzzles, etc.
because the players are brilliant. Then, to offset the INT penalty (in 5E), they rely on other PCs to make the Intelligence checks with their bonuses and even take Resilience for INT saves, or choose classes (like Rogue) with INT saves...
This is when I, as DM, step in. Your INT 8 (or lower) PC probably won't think of the things you, as a smart player, would. I might require you to make a check and if you succeed I'll allow the PC the "moment of brilliance" the thought represents. If you fail the check, you can't have your PC use the idea or whatever.
The reverse is also true. I've played with many players of average (or slightly below) intelligence. They then play wizards or whatever with INT 18. Often enough, such a player might ask me "I can't figure this out, can I roll for my PC?" because we all understand the INT 18 PC
is smarter than the player who is playing them. So, I allow them to make the roll and if they succeed, give them a hint or have the PC come up with the idea for them.
For example, I have a player who is very introverted and has a hard time speaking out, lacking confidence, etc. but he LOVES playing Bards and Paladins, both typically high CHA classes. He understands such characters are capable of doing things he likely wouldn't be able to, so he has the benefit of getting to roll for his PC to do things (such as convincing guards to let them pass), which he messes up when trying to role-play it.
Anyway, we use physical abilities to represent our PCs because we aren't
actually in the game to do physical tasks ourselves. But even though it is a role-playing game, I don't feel players should be able to use their own intelligence, speaking skills, etc. to overcome PCs with low INT, CHA, etc. If we allow the PCs physical abilities to define them (in whatever way the game dictates), we should do the same with the mental abilities IMO.
If you prefer to run your games differently, no issues obviously, but hopefully that explains why I run my games the way I do.