The LG does for sure have a bit of leverage if you attach it that way - its kind of like a comparison to the Kimberwicke - a little bit of leverage without going to a full blown curb or pelham.
Bitlesses are comparable to bits somewhat in effect - aside from pressure on the mouth.
Sidepull, nurtural/Dr.cook style bridle = snaffle
LG (just the round, no shank), Floatation, standard bosal = Kimberwicke
Hackamore (west or eng, anything with a shank really) = Curb, pelham, gag
A rider with bad hands will do damage whether they are riding in a shanked bit or a shanked hackamore. A horse who doesn't listen to the snaffle may or may not listen in a sidepull either, its all horse and training specific (and that is a whole other ball of wax!) Bitless fanatics who feel a bit is cruel do need to be careful, because a hackamore with a long shank can do terrible damage to a horse, just in a different way than bad hands on even the mildest of snaffles.
My suggestion would be that if your horse is strong in the Nurtural, you can certainly try something like the LG, but you may still have the same problem. If so, yeah, probably a training issue.
Certainly I don't think trying stuff like this is a "gimmick" - if that's the case, surely a saddle and bridle are gimmicks in the first place. I like to see a horse going in whatever makes him feel comfortable and the rider in safety and control. I don't, however, appreciate seeing horses with flashes, gag bits, tie downs, martingales, etc - That's overkill in my opinion - but hey, the olympians do it, so what do I know?
I want my horse to be completely obedient in every situation, in my perfect world he will be snaffle or sidepull soft in every aspect - but hey, I get excited for XC, why shouldn't he? :) For those days, I'll appreciate having the little bit extra a mild leverage hack has in store for me.
Yikes - sorry that got long - too much caffeine for me today!