Heavy actually does penetrate well, assuming everything else is correct (tuning, sharp head, etc.). Do you need exceptionally heavy on whitetail? What is heavy?
The young lady I referenced earlier in this thread was shooting arrows that were over 16 gpp. Were her arrows heavy? They were 400+ grains. Heavy for a 25# draw, but not heavy in general.
I know one deer she killed was approximately 25 yds away--her dad stepped it off at 26 paces.
What's a "rainbow" shot? I have a selfbow that's pretty dang slow...but I've won tournaments with it, including the Howard Hill (twice). I have another that was probably even slower that I won the TN Classic Selfbow Challenge with--shot a better score with it than I did with my much faster longbow and recurve.
Point being, there are few if any absolutes. What is heavy, what is fast, etc. depends on lots of variables.
Most won't have to obsess over arrow weight, F.O.C., etc. to kill deer cleanly...but if that's your cup of tea, that's fine too. I have no idea what my F.O.C. is, but I shoot through stuff so I don't worry about it. If I ever get to go on a really big game hunt again, then I will pay better attention to such things, especially arrow weight.