Missed this initially, but I think seeing it as 50 is the wrong way to look at it. It's 20% more damage, which is significant. Depending on the power a second recharge could indeed have a dramatic impact on damage too, but will a second accuracy increase the powers overall damage by 20%? That is extremely unlikely.
Sure if the comparison is 2 lvl 25 IOs vs 3 lvl 50 IOs but if you are looking at 2 lvl 50 IOs that is 83.32% enhancement which gets you 272.2 dmg an extra lvl 50 IO will barely get you more than 20 more points of damage!
Which is still about 7.5% increase in damage
That is a TO worth of improvement & you're not even getting that when you're under the influence of other damage buffs. Lets use a baseline of 50% fury, if you're only at 50% fury(which gives you a 100% damage boost) that 3rd lvl 50 IO is only giving you 3.75% damage increase to the specified power(KO Blow in this case) being at or above 75% fury is the norm imo.