[gralx]

Fair point. But 90% of Linux submissions are corporate, last I checked. Corporations (usually) do a lot of internal testing before submitting, and then maintainers have to review submissions. This is long before the public ("beta testers") has to deal with any bugs.

And that's only the kernel. Distributions and their package maintainers have their own quality controls, as do cross-distribution upstream developers. Public bug trackers (beta testers) are a complement to these. The division of labour in quality control of Linux systems is fine, diverse, and of variable effectiveness before beta testers come into the picture.