I'm a sorc healer, so I'm going to try not to get too confused by the different names for the same heals. I'll go with "bubble," "circle," "hot," "channel," "big," and "personal." Plus "crit-bonus" and "resource-management."
So you can certainly use circles in most of these fights, but they have to be predictive circles. Essentially, you have to know the fights well enough that you can guess where people are going to stand when they take damage. This sounds a little crazy, but it's really not. In fact, if you drop your circles in the right spots, your DPS will gravitate towards them, thereby making them even more effective.
Kephess is one of the easiest ones to do predictive circles. Even before he picks a target during phase 1, you can tell which lightning tower he's attached to. Go there. Drop a circle. The tanks and DPS will come to you, bringing the boss. Everyone will be in close proximity so that when someone is chosen by Kephess, they don't have far to run. If the circle's already down, you're not waiting 1.8 seconds before you bubble them and then channel heal them.
For the Dread Guard, you'll want your circles either near the boss or away from the green doom-circles. This is largely true for the Writhing Horror as well, and there are some obvious places for circles with Operator IX.
For TFB phase 1, drop a circle at the tentacle, then focus heals on whomever is dealing with spit, alternating with the tank. The maintenance from the circle will help keep the tank more level while you direct heals at the ranged. If you're the one dealing with spit, you can easily use your personal heal. For phase 2, circles are mostly useless and nearly impossible to place well, so just use your hot, your channel, and your big heals. You'll also need to use your resource-management ability after it procs off your channel, and you can use your personal heal to counter it.
Note that there is no shame in being healed by the other healer, especially after using resource-management. You'll recover faster if they heal you. They'll recover faster if you heal them. Cross-healing is love.
Don't forget about your crit-bonus ability. If things are going poorly, you can do a ton of healing relatively quickly by burning it, then dropping some big heals.
Force speed is also your friend. If you can get to where you're dropping your predictive circle very quickly, everyone will benefit. And, for the most part, if you actually are where you belong, the raid will follow you. You need a lot of raid awareness, just like a tank, although you'll be paying attention to different things.