> On the positive side of this, research papers by competent people read very clearly with readable sentences, while those who are afraid that their content doesn't quite cut it, litter it with jargon, long complicated sentences, hoping that by making things hard, they will look smart.

I often find that to be true. Another important factor is that research skill is correlated with writing skill. Someone who's at the top of their field is likely to be talented in other ways, too, and one such talented is making complex topics easier to understand.