IIRC, LaRussa batted the pitcher 8th and a position player 9th mainly so he could bat Big Mac #2. "The Book" agrees that your 9 hitter should be better than your 8 hitter if you stack the top of the lineup with hitters like Acuna and Freeman 1-2. Since your 3 hitter comes up so often in the 1st inning with 0 men on and 2 outs, he should be a lesser hitter than you 4 and 5 hitters.
For the most part, bottom half hitters are all so interchangeable that it doesn't really matter who hits 8 or 9 (as long as they aren't the pitcher). Ender 9th vs RHP and Camargo 9th vs LHP is probably just as good as any other order in any practical sense.
If anything, a slower runner in front of Acuna is preferable since he will be scoring frequently on HRs anyways...you ideally want fast guys to steal in front of singles hitters, and not risk getting thrown out in front of power hitters. A SB is much more valuable with Ichiro/Gwynn batting than with Bonds/McGwire batting, for example.