I don't dispute that, on the whole, the FBI does appear more professional than the ATF (I would even go so far as to say that the ATF seems to act as the personal brown shirts of whatever administration happens to be in place at the time). The questions, however, that come to mind are why is this the case and what would prevent the FBI, DEA, or whatever other federal agency the ATF might be absorbed into from becoming just as bad or worse if the ATF were dissolved?
The real problem, as I see it, is that through a series of poorly written and thought-out laws, we have given way too much discretionary power to unelected government bureaucrats who can get lost in the alphabet soup of federal agencies. I think that the ATF is probably one of the agencies most prone to abuse its power because the set of laws it's tasked with enforcing are some of the most vague, poorly written, and granting of discretionary power. I fear that, unless we do some house cleaning with the way the laws are written first, dissolving the ATF would only result in trading one abuser of power for another.