Somehow I kind of agree with both of the above two posts in some ways and disagree with them in others, which has led to me figuring out my own thoughts on Mt. Coronet properly.
I'm hesitant to say that Mt. Coronet's concept was actually particularly good for one reason and one reason alone: nothing's at the top of it. Well, you have a couple of routes, Lake Acuity, Spear Pillar, and Snowpoint City (which as I pointed out in another post is an awesome location). But that's not enough -- in the end, the payout is the finale of the Team Galactic plot and a gym badge, but as Mt. Coronet is the most central part of the region and a location the player visits countless times, the most central part of the game should be located there too. The Pokémon League.
Most players aren't really playing Pokémon for the exciting conclusion to the story. Particularly in Gen IV, where the best way to sum up the story is "perfectly serviceable", the story really takes a backseat to the gameplay. Therefore, the most exciting, most challenging gameplay -- the Elite Four and the Champion -- should take the most work to get to. And the games kind of understand this, because every game in the series has Victory Road, as a preliminary challenge before the final one.
But imagine if Victory Road were truly a gauntlet. A gauntlet the player begins working on right after the first gym badge by smashing some rocks that stay smashed, and then the player returns to throughout the game to use more HMs and clear the path even more. Move some boulders with Strength, cut a tree on a low altitude arboreal area, surf over a body of water or go up a waterfall to get to a location that Fly can later be used to get to... it's still a challenging dungeon of puzzles that requires HMs to progress through, but in the end the player can climb from the bottom to the top with no HM use at all (or perhaps with a choice of either Surf/Waterfall or Fly) meaning the player can fight the final trainers in Victory Road with their true team of 6, no HM Slave necessary. Spear Pillar, Snowpoint City and the like can still all be here of course, but above any of them is a final part of the mountain where Cynthia awaits.
I think that if that were the case, I think it would be difficult to criticise Mt. Coronet/Victory Road too heavily. The issue right now is payout per effort invested more than anything. Naturally, ideas like what Pikachu expressed above would help to refine and better harness the potential of the area down to the minutiae, but with this one small shift in the overall concept of the area, I think even if Mt. Coronet were the exact same as it is now + the additional area, it would leave a much more positive impression on the player.