Re: if it works
He called it a measure, not a silver bullet to fix all debt. And on that basis I think his point is strong. Quite strong.
The sorts of organisations* that don't value unit testing** are highly correlated with the organisations that are too focused on the here and now to allocate time to resolving this technical debt.
It's understandable at one level because resolving technical debt is expensive. The only thing more expensive is to not resolve it and then attempt a fix/improvement. But don't expect the business to recognise that the week spent on fixing some deficiency here has saved them two weeks on other projects over the following 6 months.
*I speak of organisations because individual developers within those organisations may well be pushing the proverbial uphill trying to get the business onboard, but if they can't be convinced of the benefits of unit testing then they are likely to see any attempt at technical debt reduction as developers taking liberties with valuable company time.
** By value, I don't mean platitudes about their merits. I mean actually invest time into doing it, as well as investing in some sort of ci that runs them on every commit, as well as actually being prepared to rewrite code so badly coupled that unit testing is nigh impossible, as well as actually using the facts about whether an individual developer is consistently decreasing coverage as a KPI at their performance reviews.