Why recreate the base from assembly on sandbox if you have assembly? Instead of that you hould just forge on the assembly. it would be like saying go make assembly on sandbox. It wouldn't give the same feeling because sandbox is ruin like while assembly feels real. It doesn't make sense to recreat something on the default maps. This is an example: I originally planned out my map essentials on paper, but I couldn't decide to make it on foundry or sandbox. So I thought for a couple minutes and figured out my map looks alot like the top floor of the bases on assembly. I went into forge on assembly and blocked off the map with lift blockers and then added weapons and territorries. I could of spent 2 weeks recreating that on sandbox. It would still be good, but it wouldn't feel the same and would be harder to make. So the question is; Would you rather recreate something thats on a default map or just use that map? Personally I would use the map that has the geometry already on it.
No I wouldn't bother, if it's already there for me to use, why not take that shortcut and use it? Also, how is this a guide?
The Pit, I can see not using because of the Pre-DLC disadvantages and Assembly must've been hard to forge on. I do agree though that it would've taken a lot longer to forge that whole Essentials map on Sandbox/Foundry than block off a few things.
Let' say I want to do like you said and remake the sword room. Let's say I won't add or subtract anything that is already there. That is one part of the map. You may say "You copied 'The Pit'!". There are so many things to take in account when you look at a map. The location of the room, advantage/disadvantage it holds according to how the rest of the map is, and the accessibility according to the rest of the map are some of these things. Building my map on 'The Pit' keeps more than I want. I only want to keep that room. I do not want to keep the rest. Therefore, I have to make my map according to what is already placed. The room keeps the location, advantage, accessibility, lines of sight, how it would be approached, and much more. Generally, I wouldn't copy any geometry exactly, but I can see why people would. Usually, the map designers, Bungie's in this case, get it right. Taking that sword room gets something that people feel Bungie got right.
Because if you block off the sword room in the Pit, you won't have that big of a map now would you? And just because you like the sword room in the pit, doesn't mean you like the rest of the map.
The reason you would make a certain part of another map (ex The Pit: Sword Room) is just that. You want a part of the map you like. You don't necessarily want everything on the Pit. And Pre-DLC maps don't have the advantages that Foundry and Sandbox have.
The same things Sweeney stated apply to that. If you wanted to remake it on 'Sandbox', than you go on to add what you do like.