An approximately 4 in 10 chance every minute is pretty good if you've got a power loaded up with 5 different procs (for my rad/sr sentinel, Neutron Bomb is my choice for this). If you've got more than one proc-bomb going, it can be surprisingly effective.
But if people are really obsessed with doing the "most" damage above all things, they need to play a Blaster or Stalker or Scrapper. I want to do a decent amount of damage, but doing the "most" damage is not a priority for me. I'm more concerned with building my hero/villain to represent the character concept that I'm going for.
I also tend to view Sentinels as a support class that supports in a pure combat role, so I'm expecting tanks and blasters to have most of the AOE issues covered in group combat and the Scrappers and Stalkers to zero in on the heavy hitters to bring them down. My job as a sentinel is to lend combat strength to whichever of these needs the most support, be alert for when squishier toons need to be defended, and otherwise just blast and batter down foes as opportunity provides.
Of course, the reality is, combat in CoX is almost always less tactical and more frenetic and chaotic than that, but I do my level best to perform the above-mentioned functions and I enjoy doing them.