> Robust, comprehensive libraries from reliable vendors

Hah! In all my years the biggest, most difficult vulnerabilities/problems to remediate all came from vendor-made (90% of the time closed source) software. With the free, open source stuff the problems are usually very minor but even if they're BIG we'll pretty much always get fixes and deploy them faster than if we had to wait on a vendor.

The more popular the OSS the safer it is but even niche OSS tools/libraries are easier to work with by definition because we can look at and modify the source to correct the problem even if the original maintainer hasn't gotten around to it yet. This is actually a big reason why Python is preferred where I work: The code is inherently visible and fixable.