Through the bank my experience is that a technical background with someone growing into a leadership role ultimately creates better results. People whose only skill is "leadership" tend to perform pretty badly.
But the Peter principle, doubtful if it even can be taken seriously, doesn't say anything about this specifically.
I don't know anything about Eich, but I don't really see how he would have been bad for Mozilla as a CEO. He had some controversial views as some have reported, but I don't really think that would have been very relevant, especially if so many people disagree.
All that aside, that the execs at Mozilla get millions and they still lay off 70 people is bad leadership. Really, really bad leadership. And the recent focus seem to underline that failure in my opinion.
Mozilla has done incredible things for the net and technology. Sadly, I think this is subject to change.