Very good points here, especially your last point

As you increase the complexity of a system, it makes sense that your chance of vulnerability increases. End of the day, open source or not, you will never beat basic algorithm principals and good coding practice.

I would however argue that just because closed source code is possibly reversed doesn’t mean it’s easier or as reliable as having the source code. As long as corporations have an interest in possession there will always be someone striving and spending ungodly amounts of money to keep their castle grounds gated heavily which makes securing them en mass much harder and slower