Nobody's playing for money or fame, so there are no overarching rules.
This is a distinct lack of understanding towards what motivates people to play games. Some do it for money (e-sports), some do it for fame (achievements, speed-runs, e-sports again). We each have our reasons for playing, and they're not always the same.
Single player games are for fun and practice. Why do you think that world Chess and Go masters aren't rated against machines, but rather against other players? Because it's only in fair competition that "better" matters.
I believe it to be ignorant to consider something like this. It takes us back to our motivations for playing games. Some enjoy engaging in social activities, be them co-op or competitive (multiplayer), others like solitude and playing alone (singleplayer). Each game sets out to deliver an experience the developers want to pursue. I do not believe Dark Souls 2 was developed to be practice for its PvP, or Starcraft 2's campaign to be practice for its multiplayer. Of course, you are free to see them as you wish. We each experience games differently.
Why do you suppose cheat codes are built into so many games?
Because it's not up to the game-maker to decide always how the player should enjoy the game.
Most cheat codes are built into the game during development in order to aid the developers in testing mechanics and features without wasting a lot of time (debugging). That they are left in is a service to players, but I have a hard time looking at them as a valid option of play (especially since they're almost never advertised within the game).
The goal of the developers is to create an experience (what you get from the game) by using gameplay (what you do in the game). You can't force the player to enjoy it the way you want to, but the aim is to create opportunities for that.
I don't need any TBS to be easier, but the OP wants to take away powerful tools from the game just because he doesn't want to use them, when not using is - literally - as simple as using a toggle. Don't toggle on (select) both of those talents. The argument "if something is OP don't use it" is absolutely valid.
Another development goal is to offer the player meaningful choices. That means, each choice should be valid in its own right and it's up to the player to decide which better fits his play style. Having one choice that is clearly superior to anything else breaks the balance of the game. Why would the player choose an inferior tool? Why would he act in a masochistic manner?
Here is where you balance the dominating strategy in order to allow the player to have meaningful decisions.
Singleplayer games need to be balanced in a way that it is fair towards the player, and in a way that it can challenge them from start to finish. The level of challenge is of course decided by the developers at the start, together with the intended audience.
Did you really think that in a game as wildly permissive as D:OS that the only difficulty adjustment was a global switch? That's not imaginative at all.
It's great to have games where you can be creative in your approach at handling the challenges presented, but that doesn't mean you should give the player the "Sword of InstaKills" and expect him to never use it because it will ruin his experience. That's bad design.
Magicka is a game that comes to mind in terms of having a huge amount of options at your disposal. Even so, you ended up using certain spells more often than others due to their power and efficiency (Earth... :P). I believe this hurt the variety in the game to a certain degree.