"Factories are skipping QC and sacrificing quality in favor of volume, and also scammers are trying to cash in on the skyrocketing demand" is way more likely than "China is making deliberately faulty masks". Come on now.
It's a meaningless thing to debate. To the extent coercion comes in to play, trust breaks down, so you can never know what's really going on. That's why bullies lose in the long run, but probably so does everyone.
You haven't seen the videos maybe? People spitting in masks (in China, purportedly) and doorknobs and elevator (in Europe, purportedly). Not a proof and not directly related but I wouldn't put it past China. It shocks me when they claim they have 0 new corona virus cases. If they're lying about something as basic as this, what else are they lying about.
There's been multiple people in the US coughing on lettuce, lick produce etc. Does that mean you wouldn't put it past America that masks exported to Canada will be laced with covid?