>Many lower quality teachers successfully avoid much or all of that unpaid work, especially in situations where they have strong job protections (tenure)
We'll need citation for this too.
And defined benefit plans are quite desireable and becoming rarer, and have tended to be more stable in the case of market downturns.
On the citation question, I don't have more to provide than experience from relatives who are teachers. It's quite well known that many bad teachers are quite entrenched, and those that realize their level of employment protection thread a good needle in terms of avoiding unpaid labor. It just requires caring about the job and results less, and many situations can push teachers towards feeling this way such as burnout (which can come from earnestly trying too hard and suffering from too many unpaid hours grading, etc.), the fact that there is basically no monetary incentive for good performance (everyone's on the same pay ladder generally based on level of education + years teaching), dysfunctional administration (at the school and/or district level), lack of good colleagues, etc.
This conversation began with concrete numbers, and if you want the initial presumption to stand you're going to have to end with them, too.