As just one example, they make the point that Sweden's recently mortality rate is pretty close to Finland and Norway, and show a graph of rate of excess deaths per 100k people, showing Sweden at 0.06 and Finland and Norway at 0.04.
That's 2000 additional excess deaths in Sweden per 100k people than their neighbours. This equates to an additional 208k+ people that would die if the full country was infected, based on the presented mortality rate data.
If we want to be scientific about this point, we'd have to ask several questions to actually understand whether those numbers are meaningful in the way the author suggests:
- Is it typical for Sweden's all-cause mortality rate to be 50% higher than its neighbours? - If not, what is the typical difference? - Could there be other unaccounted-for confounding factors?
That these questions and answers were omitted I think demonstrates pretty clearly the author hasn't fully considered the point they are attempting to make, or suggests that these questions were not answered because by answering them it may undermine the point they set out to make.
Mask quality is definitely a factor, but can't be the major factor, unless people wear masks 100% of the time and never take them off outside of the house, which we know it's not true. There is also the "eye protection" factor, which seems to exist.
If you look at the overall global picture - location, climate, size, population, demographics, education, GDP, mask mandates, ... - there is no clear conclusion, it's a causal mess.
It's safe to say that at this moment nobody can predict where a covid wave will hit and how big it will be, outside a very general sense - that it might be bad in the winter in unvaccinated places.