As you (hopefully) realize, the average person doesn't want to spend time to understand 20 different settings, especially if they involve math. With that in mind, I propose the following redesign of deck options:
It doesn't get any simpler than this!
In all seriousness, though, I don't think that FSRS (or any similar algorithm) can come anywhere close to mass adoption without:
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Making FSRS the default algorithm.
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Hiding the field with parameters, as well as anything that has the word "parameter" or "optimize" in it.
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Hiding any numbers other than desired retention, which should be the only number that the user can see.
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Automatically suggesting the optimal value of desired retention so that the user can turn their brain off and just go along with the suggestion.
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Automatically, periodically optimizing parameters without notifying the user.
This is what it takes to even begin reaching mass adoption (of course, other elements of the UI that aren't related to the algorithm would also have to be redesigned). In its current state, FSRS is difficult to use, even for advanced users.