Wow, that was an extremely helpful post. I'm going to have to think very carefully about what you've said, but here are my initial reactions to your advice:
First of all, the Demoman exploit. I didn't even think of that, but now that I know about it, I can see that it clearly needs to be rectified. Fixing this is now top priority for me, because being able to shoot into or out of your spawnroom is just ridiculous.
I intend to more or less completely redesign that building with the long Sniper sightline. I actually intended to entirely rework the underground route and add a staircase up to that building from it, hopefully allowing for a less terrible route. The idea of the underground route was to have a low-traffic "flank" that would allow players to sneak up on their enemies from behind, especially if those enemies were deeply entrenched near the point and their defenses could not be broken. That's why I said it was a "Scout and Spy route". What I didn't predict, however, was that the route would completely suck for anyone other than a Scout or Spy (well, it still sucks even for them, but at least Scouts can get out of there quickly). The route can be used as intended, as a stealthy flank, but players clearly weren't using it that way, so it's my job is to figure out how to redesign it in a way that encourages players to actually use the route occasionally (although it's definitely not supposed to be a major route). I really don't want to have to completely remove this route if I don't have to, because the unique idea of going right under the point is one of the defining features that make it stand out.
You mentioned also that the stairs to the underground route are "outright unwelcoming". I'm not sure if you mean that they are ugly or that they look like a bad route to take (although I'm certain both are true), but in either case, how do you think I ought to redesign them if I want them to more or less retain their original purpose?
Although I thought very carefully about your suggestion to make the point underground, I'm not terribly keen on the idea, mostly because it would require changing the entire level, more or less. My original idea for the Cap was to make it difficult to hold for the entire round, ensuring high turnover rates and many rounds where one team just narrowly defeats the other. If there's one thing I got right in this map, that's it, according to the Feedback data I've received so far. The fact that the cap area is somewhat lower than its surroundings makes it a terrible place to defend from, which forces players to find other places to defend from once they've capped. The pergola above the Cap, however, protects it from above. I guess I don't want to change that part of the map because, if I did, it would change everything, and my entire original vision for the map would have to be thrown out. I hope that I'm not being stubborn by trying to hold on to my original intent. I'm trying to fix the map in order to bring it closer to my original vision, not completely change that vision (unless I really have to).
Now for the lack of verticality. I didn't even notice just how flat my map really was until you pointed it out to me. Non-jump classes mostly stay at about the same height no matter where they go in the map. That's rather boring, both visually and and gameplay-wise, so clearly I need to find a way to add some more height variation. You mentioned allowing players to walk around on the roofs of the buildings near the spawnrooms. I am very opposed to that idea; I don't want to replicate the spawncamping nightmare that is Harvest. I like your idea of making a ramp and/or staircase where those divider walls are currently, but I hope that doesn't make it easy for Soldiers and Demos to spam the spawnroom's exit doors, but there are other ways out of the spawn, so I think it would be safe to implement your idea.
Getting back to the Sniper sightline problem, it's clear that there are sightline issues throughout the map. However, even now, Snipers are always very near to their target, and usually very vulnerable (except for that one building you pointed out), so I'm wondering if further reducing sightlines would make Snipers close to useless in this map. After I fix that one sightline you showed me, I'm going to be careful about blocking off many more.
There are a few other problems I've perceived as well that I'd like to address. I've seen that mini-sentries are very overpowered if placed anywhere near the Cap. That's a very frustrating problem for me, because I'm of the opinion that minis are very overpowered. I think it's exceptionally difficult to try to balance something that you feel is unfair to begin with, so the only fix I can think of right now is making the Cap area somehow less open.
Also, I can see that Soldiers and Demos seem potentially overpowered at the moment, but if I make the other changes I've talked about here, that problem should be fixed. Also, I've had a few people tell me the level is slightly too big. My solution to that right now is just going to be to greatly reduce the size of the spawnroom, and center the playerspawns in the middle of the room so that one door isn't more useful than the other.
Cripes, that was quite an essay. Even so, I'm glad I've gotten my opinions out there, because if people know what my intentions are, they should have a far easier time helping me out. I just want to say that even though my map is riddled with problems right now, it's been an incredible experience so far, and I'm infinitely greatly for what all of you have done to help me. Even hearing feedback like "your map is alright", or "your map has potential" is extremely encouraging to hear from a community like this. The fact that you guys didn't immediately tell me "your map sucks, just scrap it", and instead actually thought it might be good someday... well, that's some serious motivation to keep pressing onward with this map.