Very much agree with this (although I can't say anything about the maths involved).
As someone new to the test server and arriving during an event I think that the current version of the attraction system disadantages newer players during events, If we assume that when RNG rolls "girl attraction" it picks one of the girls you need to get then rolls how much you get this won't be good for new people. For example, I have just got to world two and therefore I have 4 girls to obtain (with the event girl having the lowest attraction drop rate to boot). On my main account (on the final world with everyone up to Finalmenica finished) I would always be getting attraction for the event girl and my chances are better!
To rectify this I would suggest one or a combination of either the four below (each will probs have pros and cons)
1) Make event girls and normal girls independant - so you have cash, event girl, normal girl as options.
2) Up the chance of the even girl dropping attraction (and probably the amount given)
3) Maybe still leave an option in to get event girl in 1 battle
4) Have it so during the event, until the event girl is romanced they are the only attraction that drops. Once they are done it goes back to normal. You could keep the amount dropped relatively low again (still i'd suggest a tad higher than now) to make it take a while but it would give a much better chance of getting them.
None of these ideas are perfect but it is food for thought.