Necro, but I just realized that we may have been asking the wrong question here. Instead of percentages of spells dedicated to removing other permanent, I'd like to pose the following: what is the ratio of spells that can remove creatures to the number of creatures you have? No need to take into account things like 2- vs. 3-damage burn spells.
The context of this question is, of course, that I've been struggling with removal in my cube recently and felt like I had way too much even at 89 on average out of 384, a reasonable 23%. However, on examining my "target-to-spell ratio," I realized that I only have 144 creatures on average, meaning that my drafters can answer at least 60% of creatures. My ratio is therefore 1.61 and I suspect it's lower than average. Thanks in advance!