uhm, yeah if xou really want to find excuses for using certain skills, yes, you can push them all if you want.

thing is, the better the group, and the higher the overall dps of that group, the less need for all that extra stuff. well, if its an over the top group, you wont find yourself casting a single heal once.
there's a nice trick with holy though. just wait a second before casting the next one. you'll lose some dps. but as a trade you keep trash stunlocked. which on the other side means, no dmg on tank. which means: if dps are high, a smn in group with his handy shadowflare and the tank knows his stuff, yeah, you wont need to heal anything except maybe tankbusters or maybe some crits on your tank.
cool hu?

i'll repeat myself: this game isn't designed for this trinity setup. and i'm not sure if it ever will be.