"True pro healers" choose to use the tools that enable them to do their job most effectively. If you find you are able to maintain awareness of and appropriately respond to any scenario as it arises without add-ons, that's fine, but it doesn't detract from those who find their performance buffed by using them.
For me, I find that so long as the influx of information is controlled and manageable, more information allows me to make better decisions faster. Despite the wonderful improvements in Blizzard's default UF, I find it lacking in certain aspects. So while I can heal effectively with them I am a superior healer by using Grid (and Clique, but that's just preference over mouseover macros) configured to present the information in the way I can assess it fastest.