I do think that contributing fuzzing and quality bug reports can be beneficial to a project, but it's just human nature that when someone says "you go ahead and do the work, I'll stand here and criticize", people get angry.
Rather than going off and digging up ten time bombs which all start counting down together, how about digging up one and defusing it? Or even just contributing a bit of funding towards the team of people working for free to defuse them?
If Google really wants to improve the software quality of the open source ecosystem, the best thing they could do is solve the funding problem. Not a lot of people set out to intentionally write insecure code. The only case that immediately comes to mind is the xz backdoor attempt, which again had a root cause of too few maintainers. I think figuring out a way to get constructive resources to these projects would be a much more impressive way to contribute.
This is a company that takes a lot of pride in being the absolute best of the best. Maybe what they're doing can be justified in some way, but I see why maintainers are feeling bullied. Is Google really being excellent here?