Is progressive content or the community to blame for player skill gap?

[Dorander]

Skill gaps are related with personal motivation and interactions. In addition to practice and experimentation, most good players in most multiplayer games interact with relevant communities and partake in, or at least look at theory crafting. High level learning doesn't come from in-game tutorials.

This exactly. Lack of motivation to actually learn about anything is why there is a skill gap. That's why there is such a divide between the so called "elitists" and "casuals." The "elitists" take the time to learn how to play optimally in all content, while everyone else just decides they are going to wing it, and get hostile toward anyone who questions their play style.