Since an effective access control would by definition not be subject to circumvention, there is no conceivable situation where someone might be guilty of circumventing an effective access control.
Well, the thing YouTube does (whether you call it an access control or not) does actually have a measurable "effect" on people. It makes those people seek out third-party tools when they don't perceive any other reasonable way of downloading the work. So by that logic, it's pretty effective.
Nothing is ever 100% effective -- even the best encryption is technically a compromise -- other than OTP. YouTube just happens to be on the low end of effectiveness; the third-party tools likely wouldn't exist if it were on the high end. But I guess even slight effectiveness is enough for DMCA purposes.
https://www.merriam-webster.com/dictionary/effective
An ineffective access control? Perhaps, but the DMCA doesn't mention those.