I agree somewhat but mainly from the perspective that they should have been careful of what they say because of how this has been taken, I would say the instruction on reasonable doubt is more fundamental to the jury's actual decision making than the instruction not to be swayed by emotion or sympathy.
The instruction on not being swayed by emotion or sympathy is of course important but people are human and many will be swayed by it, but the instruction on reasonable doubt is fundamental, it's the burden of proof. They're told that no matter you think, if the burden of proof is not met then you cannot convict.
Let's say this had been treated like a juror misconduct issue and there had been a proper inquiry I would fully expect a failure to apply the reasonable doubt standard as a much more serious issue than a juror admitting they were swayed by emotion and thought she was a good mother.
It's also quite reductionist to just put it down to them saying she was a good mother, they felt like this due to the evidence presented to them, from that standpoint if you think well the evidence showed that this person was a very good mother many are going to think that the killings then showed an extreme departure from that so something extraordinary must have happened.
This is only an issue if the jurors stopped completely and that point and said lalalalalala I'm not even going to listen to or consider the prosecutions theories, but if they listen to them and consider them and the prosecution still hasn't convinced them beyond a reasonable doubt then that doesn't mean the jurors haven't followed instructions.
And Dr Mack was an absolute shit show of a witness for the prosecution. Heilbrun and Saathoff were better but I thought some of what they said was deliberately misleading and they certainly didn't convince me that she was capable of obeying the law despite her mental illness.