Host is honest with their weights. When we ordered ours from Host the general manager sat down with us and could tell us exactly what every option weighed and after filling out the build sheet he told us what it would weigh within a very small margin of variance. In general I wouldn't place much value in manufacturer claimed weights but Host really does break it down and stand behind their numbers.
The base weights of the Lance and the Mammoth are comparable. The mammoth with zero options weighs just under 4,000 pounds. According to Lance website they are at just over 4,000 pounds with std equipment.
The Host has larger holding tanks but you can always control how much water you put in.
Ours sticker is at 4,361 (without generator and rear sofa (putting a recliner)