The main issue now is that, in my view, the layout isn't particularly suited for KOTH. Virtually every successful KOTH map, in terms of gameplay, offers a center point that is protected in some way, with a finite number of entry points (Garbage Day, Loader, Harvest, Oilfield, Lighthouse, to name a few). Tomb's point is exposed to virtually the entire map, and it seems like an exercise in which team can spam the point the most. While it won't fix the issue, reducing the capture time dramatically would help. Loader and Garbage Day have short capture times and it makes for fast-paced, interesting gameplay - though the rounds tend to last longer as the point's handed off between the two teams much more frequently.
Two other major issues, IMO. First, there are extreme lines of sight for snipers in every area of the map. I think you should add walls or obstacles in the side routes on the "surface" (non-sunken) areas of the map to break up LOS. Secondly, the steps impede movement too much. In forcing players to pause and jump, the steps make players incredibly vulnerable and frustrate attempts to rapidly escape the area below. Snipers and other players up on the surface have free range of motion, but the steps turn the capture point area into a fish-in-a-barrel situation.
There are at least two ways of addressing the layout issue - you could add more structure around the point itself. You already have two small walls, but their protection is very minimal and it limits visibility when you're on the point more than it helps guard you against spam. You could add a roof over the point and space the walls out a bit further, aligning the entrances with the sides of the map (rotate the walls 90 degrees).
A second method is basically vertically inverting the map. Obviously, this is a very dramatic change, but one to consider. As it stands, it's virtually impossible to defend yourself from players perched up on the surface of the map. When shooting upwards, especially with rockets/pipes, your aim has to be perfect, and you lose out on splash damage, killing most of your effectiveness right there. For other weapons, the distance involved combined with weapon spread reduces their damage to the point of being useless.
I think if you were to simply switch the game rules to KOTH and change nothing else, Watchtower would have much more satisfying gameplay than Tomb in its current form.