But, recently the percentage of RM starters has dropped below the percentage of RMs on the roster (if that makes sense). Take this case for example:

In 2014, there were 80 RMs on the roster (65%). But, only 12/25 starters were RMs (48%). 6 starters (24%) were non-LDS and 8 starters were LDS but did not serve missions (32%).

In 2013, there were 79 RMs on the roster (64%). 16/25 starters were RMs (also 64%). 5 starters (20%) were non-LDS and 4 were LDS but did not serve missions (16%).

In 2015, I project 78 RMs on the roster (63%). Just 54% RMs, with 24% non-LDS and 22% LDS non-mission.

However, in LaVell's era, I'd bet that the number of LDS starters on a given team would have been even lower than 48% in each of the years he coached. I don't know how you can quantify that, though.