Just a piece of advice for my last message to you in this thread - it is extremely difficult to learn and develop (in every context) while one maintains the "I know everything" attitude.
I would still pick the 18 y.o. and strangely enough the reason why has nothing to do with elastics. I saw Alonso mention it in a post of his that I came across recently. Maybe you can go through his posts - there's something to learn from many of them.
However the fact that we are having this discussion means that 75 as a hard TSP threshold for 19 yo draftees with increased skills would be close to optimal.
BBB: 2 (S37 S38); Top tier: 7 (S35 S36 S37 S38 S39 S41 S63); Cup: 9 (S25 S35 S36 S37 S38 S39 S40 S41 S61)