But you are arguing for the inclusion of variety, and I am arguing for non-mainquest-centricness and particular showcasing of things intended to seen early on and be pulled towards through the game, rather then have the good content be actually varied in distribution so as not to punish players not doing the main quest in this open world game, which is completely different. Ugh, I have had this conversation so many times now. It honestly baffles me that so many people miss or do not get this simple concept.
I have some of the same problem with Skyrim, except I don't see showcasing as the cause. I don't see any clear evidence that any place is designed to be a showcase. Bleak Falls Barrow is there for you to explore whether you do the main quest or not. I started playing Skyrim the day it came out, and I have spent the bulk of my time avoiding the main quest. I find no absence of large, interesting, exploration-worthy places outside of the main quest.
With or without showcasing, there will be variable place quality. Showcasing does not cause that variance. It is very probable that quest writers desiring high-quality quests will choose better-quality locations for their quests, have they the option to choose such. They do have that option. Showcasing does not give them the option; variance does. The main quest just so happens to be -- surprise, surprise -- a major quest. it is meant to feel like the biggest event in the game. Is a quest writer's location of choice for a lost artifact for solving the main quest to be a simple, out-of-the-way wolf den, or is it to be Bleak Falls Barrow? It isn't a tough choice to make, and it has nothing to do with creating an early-game showcase.
If there is a lack of interesting places outside of major quests, it is because there is too much quest, too much story, and too much plot for the game world to sufficiently provide for activities beyond the quests, stories, and plots. The main quest gets the Falmer Embassy, because the main quest is deemed important. Some rinky-dink (though still appreciated

) Radiant quest for a statuette of Dibella gets Timmy's house, for Timmy's house is all that's left after the more highly-regarded quests have staked their claims. If you set out to adventure on your own, then you are stuck with the places nobody else wanted.