I do want to tack onto Miste's most recent comment to the thread and add that while the participation numbers on logs should be taken with grain of salt due to the voluntary nature of logs, I imagine S-E's official back end tools will show a similar percentage breakdown with some small deviations (I'd guess +/- 5%). What these numbers tell me that it certainly isn't undesirable though the topic of "kit strengths" is certainly up for debate. Even if WHM isn't meta for the speed kill community, it is certainly played and played immensely.
Apparently, based on what I can see, logs maintains historical data for their logs that are relevant for the tier (IE, only using 3.4 and 3.5 clear data for Alexander: The Creator (Savage) ). You can find the participation data set here - it shows AST being the most played with SCH not too far behind and WHM lagging behind significantly.
TLDR of stats:
Alexander: The Creator recorded 37,776 healer logs with the following breakdown: SCH = 37% | AST = 41% | WHM = 21%
Sigmascape (Savage) recorded 107,798 healer logs with the following breakdown: SCH = 39% | AST = 23% | WHM = 37%
I'd also like to point out that despite how meta the SCH/AST healer comp is, the participation data doesn't reflect these meta compositions. This is in contrast with the tank meta ( WAR/PLD - participation data here ) and DPS meta ( DRG / NIN / BRD / [Fight & Group Dependent Wild Card Slot] - participation data here ). I'd like to also add a small note that despite MCH having the lowest participation numbers, they are represented in several top 10 speed kill groups currently, while BLM and SAM have no representation.
My point in all this wall of text? Even if AST/SCH brings the most raid utility and DPS to the table out of all three healers - a fair number of groups still run WHM for the safety factor (higher HPS throughput and eMP Pool). We're less than two weeks away from patch 4.3 and despite some comments about how "progression is dead" at this time frame we still see WHM, argued as the primary progression healer, being used heavily. This leads me to believe a few things including there are still many groups freshly progressing into the raid or those that have cleared the raid tier will still continue to run the comfort pick of WHM because either they're more comfortable with the WHM kit or don't want to change things up so they can keep clearing the content safely and smoothly. I imagine if many of the current raiders felt WHM was unfeasible, we wouldn't see the current participation numbers that we do at this juncture.