This is interesting stuff. Nicotine is very powerful. i tried it because of a stupid gimmicky diet which claimed it increases ANP which can get u ripped fast lol lol. but i found i could stop it cold turkey without a problem. I kind of was looking forward to the challenge of crazy bad withdrawals just to say i beat them but i never had any. but from what ive read, the way of taking it is more important, if you smoke it or vape or whatever, it hits you straight away, which is what you get addicted to, that instant feeling, kind of heroin i guess? but even then, i feel the lozenges work pretty quickly too, obviously not as quickly. not sure of the science behind it. still, i'm sure smoking it is what makes it addictive though. i'd use nicotine again for performance but the idea of smoking anything just repulsive. wonder if there are other classes of recreational drugs which would be not as addictive if you took them another way.
Not sure about it helping weight loss via any mechanism other than appetite suppression but it definitely helps there. For sure the route of administration is important and you're right, that's the case for most drugs with generally the faster the route the greater the rush. It does seem that cigarettes are more addictive than other routes, even vaping and that may also be down to MAOIs (monoamine oxidase inhibitors) in tobacoo which prevent breakdown of dopamine/serotonin etc and therefore adds to the effect.
I'm unsure on nicotine, I found it incredibly useful during my finals as a wakefulness/focus enhancer when it was too late in the day to be drinking caffeine. Never got addicted or had any withdrawals but spread my use to avoid this. And nicotine in itself doesn't hold too many health drawbacks but obviously dependency is very un ideal.