I never said they were efficient - I just said they were good slayer/hr, which they are.
As I keep saying, they *may* be good slayer/hour, but Slayer and Combat are so intertwined that to introduce one side of the equation while ignoring the other would be folly.
I said they offer a great balance of
slayer
xp and gp
The phrase "Jack of all trades, master of none" comes to mind here. To use a pokemon example: Mew went from Uber in 4th gen all the way to UU in 5th gen because other pokemon could do anything it tried to do (whether it be support or sweeping) better. What you're basically saying is "Why use Salamence for sweeping when Mew has better bulk while still keeping offense?" when Salamence is faster, has higher offenses on both sides, Intimidate giving it better physical bulk and potentially forcing switches, and arguably a better typing, giving more offensive pressure and setup consistency than Mew without having to use extensive support to make it viable as a sweeper.
For support, Blissey would be a better option because of its stupidly high special bulk (considerably better than Mew's), also having reliable recovery, and having access to status-inducing moves for utility.
When you're in a "Jack of all trades" scenario, that will eventually leave you outclassed and forgotten (Pokemon like Clefable and Wigglytuff also fit here).
Now, how does that tie back to Mammoths? Well, as I keep saying: if other (lower level) tasks give you a run for your money in EXP and blow you out of the water in GP, then it's not really *that* good when you *really* begin to look at it and you're better off doing other things.
"Revenge...is like a rolling stone, which, when a man hath forced up a hill, will return upon him with a greater violence, and break those bones whose sinews gave it motion."- Jeremy Taylor