there is no such thing as better skilled healers in the sense of a parser trackable stat. The only thing that matters is that the healer doesn't let anyone die and keeps the parties debuffs cleared as well. Healers with higher skill can continue to perform that function while doing some dps and making the run go faster or by maintaining those criteria on large pulls during speed runs.

During 8 man content it can sometimes be hard to tell which healer is stronger if the weaker one is having his slack picked up by the better healer but its usually not too hard to tell who is performing better. WHM should be maintaining nearly 100% uptime on regen on the tank and getting medica II up for things like stomps or splumes and scholar should not have their fairy die by having it in the wrong location and should be getting succor up before aoe damage or maybe dropping a sacred soil. If you are familiar enough with the things healers are doing to make the run easier, then it becomes very easy to spot them when they are not there and identify the weaker healer. This is a great opportunity to coach them and let them know how they can make their own life easier.