Also keep in mind that the Big 6, er, 5, is growing less relevant in the electronic world
How do you figure that? Because I just checked the top 100 on the Kindle paid list, and only two of the top 10 aren't from the Big 5, and those two are from Amazon imprints. IOW, not one of the top 10 is from a small e-press or is self-published.
1. Sycamore Row by John Grisham (Doubleday [Big 5])
2. Silent Echo by JR Rain (Thomas & Mercer [Amazon imprint])
3. Unwritten: A Novel by Unwritten: A Novel (Center Street [Big 5])
4. Mine by Katy Evans (Gallery [Big 5])
5. Ender's Game by Orson Scott Card (Tor [Big 5])
6. The Book Thief by Markus Zusak (Knopf Books for Young Reader [Big 5])
7. Allegiant by Veronica Roth (Katherine Tegen Books [Big 5])
8. Wilderness by Dean Koontz (Bantam [Big 5])
9. Things We Set on Fire by Deborah Reed (Lake Union [Amazon imprint])
10. The Husband's Secret by Liane Moriarty (Putnam [Big 5])
The first self-published book is number 14, Our Favorite Slow-Cooker Recipes Cookbook by Gooseberry Patch.
This is one other self-published book in the top 20, and a couple more from Amazon imprints. There are no e-only micropress books in the top 20.
Three years ago, almost the entire top 10 list was self-published titles. Today, not one of the top 10 list is self-published, and all are from either a Big 5 or an independent trade press. (Yes, Amazon Publishing is an independent publisher, using the long-standing publishing definition of 'independent': a trade publisher that is not part of the big conglomerates.)
This evidence doesn't exactly support the contention that the Big 5 is becoming LESS relevant. The facts suggest that the Big 5 have regained most of what they lost when they got caught with their pants down by the speed with which e-books caught on a few years ago. They have clearly caught up to their former dominance.