Here's one problem with both "first 100 picks" and Z-Men's method; the logic is circular. The logic is:
You shouldn't take a QB in the first round, because:
People usually take RBs and WRs before QBs, because:
QBs are usually available later in the draft, because:
People usually take RBs and WRs before QBs, because:
You shouldn't take a QB in the first round.
The other problem is that average starter, worst starter, and worst player baselines are directly translatable to fantasy points for your team; it can be shown that maximizing VBD using those baselines will have specific effects on the number of fantasy points in your starting lineup--especially when the analysis is done in arrears (looking at previous seasons). "First 100" tries to use behavioral economics to predict what players might be available during the draft; there may be some argument for using First 100 baselines to select players during the draft, but it makes no sense to use to evaluate how valuable a player was in a past season.
That is, the fact that 30 RBs were taken in the first 100 picks of the 2004 draft, and only 10 QBs, does not at all imply that the end-of-season #10 QB had the same value as #30 RB. All of the adjustments Z-Men makes are already factored into the end-of-season rankings, as the players have already missed the games they were going to miss, had the breakout seasons they were going to have, etc.
So, the fact that worst-starter and other quantitative methods of measuring positional performance in previous seasons show that the top QB is usually in the top 10 overall implies that the RV and First 100 baselines are actually overstating their case, as it is difficult to see how their suggestions for draft picks would have translated into more fantasy points in your starting lineup, given how fantasy football seasons have actually finished up.
To make the point specifically, from 2004 the #9-11 QBs were Marc Bulger, Tom Brady, and Drew Brees. The #29-31 RBs were Marshall Faulk, Derrick Blaylock, and Onterrio Smith. It seems fanciful in the extreme to suggest that the latter group had as much fantasy impact as the former group.