If you look at the class choices for DnD, you can clearly see that every class has at least one noticeable strength, and at least one noticeable weakness. This is to encourage teamwork and learning to use the strengths and weaknesses of a party. In DDO, really only raw DPS matters.
And yes, the druid is capable of reasonable amounts of dps from both casting and melee, and while not perfect, can even do them at the same time. But the sp pool is also half what the sorc gets, and the spell power is reduced or non existent as well. So if you were to run through all the sp from both and add up the total dps, the druid would have about 1/4 of the total dps of a sorc. Increasing the melee ability to anything decent requires cutting back on spell power and points even further. While a druid is flexible, it is clearly not as powerful as a sorc for raw dps.
All I'm saying is that wizards and sorcs can easily be built to have absolutely no weaknesses. At that point, they are significantly more powerful than any other class in DDO (other than monk) who all have definite weaknesses.