I think it’s unclear what the effect will be if we talk in these terms.
At the extremes, sure, it is simple enough. But at “halfway”, it seems far less clear.
For example, a Tacx Vortex can simulate up to 7%.
At “Max” trainer difficulty, you’ll get 7% on a 7% hill, and 7% on a 10% hill.
But at halfway, what? On that 10% hill? We’ve cast it in terms of the range the trainer can emulate, so 50% here could mean simulating a 3.5% gradient, because the trainer can only produce up to 7%. But it could also mean simulating 5%, because that’s half of 10% and the trainer can manage it. That’s 71% of the maximum range that the trainer is capable of producing; so the “halfway” slider position becomes disconnected from trainer range.