Yes we can. Not a single post in this long thread disputes that point.
No. Many measurement systems can display a high degree of consistency while being imperfect. That said, I suspect the even the best AE systems available today are neither perfect nor consistent. But these flaws do not make them useless.
The usefullness of AE, like any tool, depends on the skill of the user.
1. If AE is less than perfect then it is giving incorrect results. If the degree of error varies then it is inconsistent and cannot be satisfactorily compensated for without adjustment to each frame. If you are having to adjust each frame, or batch of frames, with exposure compensation then you are, to all intents and purposes, shooting manually anyway.
2. If AE is less than perfect then there is a scale pf imperfection from 99% right (ie acceptable) to 100% wrong. At what point on that scale does the rate of error become so significant as to render it too ineffective to be of practical use? If it is of no use, ie the percentage of frames that are not exposed within an acceptable range becomes too great, then it is 'useless' in that situation.
Now I don't know what sort of photography you do but for my area I have to be quick, and reliability of exposure is critical. I, and several others who do the same sort of editorial work, find that AE is simply not consistent or effective enough to be used and we have all reverted to manual. Is this acceptable on top end cameras? Maybe you think it is, I happen not to, if that makes me a crap photographer in the eyes of those who have time to faff around with with exposure compensation, 101 metering modes or whatever takes their fancy then so be it, some of us have a job to do and simply cut out the middleman. The histogram and screen are our meters and funnily enough we get the results, shameless, unskilled snappers that we are.