Aside from Stuart's objections below, I think the bigger issue with your argument is that (I'm going to try to reduce the amount of notation to hopefully be clearer) even if R(AI does nothing, AI takes over discretely) < R(AI does nothing, AI takes over overtly), that doesn't tell us anything about R(AI does nothing, AI makes a paperclip), which should still be vastly lower than either of those, since "takes over discretely" is still extremely high, since the AI can't hide from itself (or if it can, the argument needs to be made in favour of that).

If some of the assumptions are relaxed, it might be possible to argue that making a paperclip is in some way equivalent to taking over overtly (although it would be a difficult argument), but with current assumptions that does not seem to be the case.