Perhaps you could offer some evidence? Dragonite's bulky is only barely better than mence, it needs at least 2 DDs to have the power of a Mence at +1 if it's running lefties , it has significantly lower SpA and can't wallbreak nearly as well, and it is quite a bit slower
Just fyi, Mence has a base attack of 135 while Nite has a base attack of 134.
Nite's defenses are 91/95/100, Mence is 95/80/80. Factoring in multi-scale, Nite's bulk is clearly superior to mence's.
About getting 2 DDs in, here's what you do:
1)Switch in free against something you will force out(this may be on revenge or on an EQ)
2)DD on switch
3)considering you got in for free at first, DD again while being protected from being OHKOed due to Multi-scale
4)Sweep
This is considering you managed to eliminate all opposing ice sharders. If not, you are still sitting comfortably at +1/+1 while their sharder failed to KO you.
Basically what I'm trying to say is that Nite is more of a bulky booster while mence is superior as a purely offensive DDer. Its more or less the same as Latios vs Latias.
..........I probably wrote this up poorly but eh.
EDIT: lol ninja'd horribly.