The one assumption I won't question is the assumption that Rika will land the 4S; without that assumption, obviously nothing is worth comparing.
Assumptions I will question:
1. Rika also normally does 3 lutzes, it's just that a minor leg injury prevented her from doing a 3Lz at ACI. If you take her WTT short from last season, for instance, where she landed her entire layout, you'd find a jump base value (+GOE)
3A = 8.00 + 2.86 -> 10.86
3F + 3T = 9.50 + 1.51 -> 11.01
3Lz = 6.49 + 2.11 -> 8.60
Add on GOEs, her jumps total 30.47.
Now, for Rika's free skate, you actually took her ACI free skate, because her 2018 NHK layout was
3A+3T, 3A, 3Lo, 3Lz+2T, 3F, 3Lz+2T+2Lo, 3S
If we take the scores that actually correspond to her NHK jump layout, we find
3A + 3T = 12.20 + 2.63 = 14.83
3A = 8.00 + 3.09 = 11.09
3Lo = 4.90 + 1.54 = 6.44
3Lz + 2T = 7.20 + 1.69 = 8.89
3Fx = 5.83 + 1.59 = 7.42
3Lzx + 2T + 2Lo = 9.79 + 1.26 = 11.05
3S = 4.73 + 1.17 = 5.90
This gives a total jump value of 30.47 + 65.62 = 96.09, a gap of 11.83.
Now, if you take a look at Rika's planned content this year, she plans on swapping out a 2T+2Lo with a +Eu+3S and then plans to replace the 3S with a 4S. Overall, she replaces a 2T+2Lo with a 4S, Eu. For simplicity, I will neglect the +10% bonuses. A 2T+2Lo is worth 3, a 4S and Eu are worth 10.2, giving her an extra 7.2 base value. If we give her any kind of +GOE on her 4S, like a +2, the same GOE will not be applied to her 3S, which the above does involve in calculations, so the net GOE gain is about 1 point. Thus, Rika stands to gain around an extra 8 points from her 4S.
The TES gap is now 3-4 points. You may make a comment about Sasha's PCS rising. However, keep in mind that Rika gave a relatively uninspired performance of her programs at ACI too, so her PCS could very well rise too. Thus, it is dangerous to try and compare their PCS scores after any rises.
Basically, the point is, if you have a TES gap of 3-4 points and a PCS gap of about 6 points, it's an even competition. Rika has three difficult jumps and one difficult combination to land: two solo 3As, one 3A+2T and a 4S. Sasha has three difficult combinations and two difficult jumps to land: two 3Lz+3Lo (which she has struggled with at times), 4Lz, 4T, 4T+3T. It's easier than you might think for either skater to mess up. Thus, my conclusion is this: if they both skate perfectly clean, which would be extraordinary, it's down to the judges. If any of them makes mistakes, it's a matter of who messes up more. I will agree, however, that Sasha is more likely to skate perfectly clean than Rika, and that is the only reason I give the advantage to Sasha. If Rika shows any ability to skate her programs consistently, it'll be much more even.