My preferred example is actually Manamune Shen.

That's the 2nd time but I'll use proper example in the future. Thanks for the heads up.

I love how the scouts of mobafire collectively use AP Garen as an example of "sure it can work, but it's ******ed."

Anything can be put to work. You can make AP Garen work for the heck of it with proper items but your build itself is already lacking. Gnar is much better as a tank/top laner that it's really hard for you to convince someone without evidence of ADC Gnar working in high rankeds or something. Even proper set of items would boost your credibility immediatly but your build is really weird and isnt't fit for ADC.

You're one of the many people to make Gnar guide and get dissapointed with the feedback. I can say with confidence that no Gnar guide will be good enough to please the public for quite some time.

No point in arguing wether ADC is viable or should be done when the guide itself is lacking so much.

I've gotten better since then and I'm Plat now, though. I reckon I'd only lose half as badly as I did back then. Although Wickd might have a few things to say about that.

To paraphrase one of the top tier players in Korea:

"Just because something goes well, doesn't mean it's the correct choice." - Lastshadow

I once made a bet that I could beat anyone below gold with a very unconventional pick just to prove that success doesn't define the viability of a pick / champ.

So, Sirell and I did a one versus one to prove it, he went Caitlyn and I went (first time) fiddlesticks AD carry (crittlesticks, if you wish). Anyone will agree with me that Caitlyn should win this, right?

However, I won. Does this mean Crittlesticks in bot lane is viable? No. Having success with something doesn't mean it's good by any means. It just means your enemy wasn't good enough to exploit your weaknesses. In this case Sirell wasn't good enough to exploit the range differential, and so have your enemies.

Proof:
https://www.youtube.com/watch?v=HMuIbe6tOUM

Your mastery tree is a fail....

Also, straight form Wikia

The Black Cleaver is considered to be a far superior item than Last Whisper on Gnar. First, The Black Cleaver grants Gnar some health, something that he needs when he enters Mega Gnar form. Second, Gnar has a lot of AoE in his kit, which synergizes well with the item's passive. Finally, The Black Cleaver gives cooldown reduction, which is useful for Gnar's long cooldown in his kit.

I've won with AP Jungle Poppy, adc Swain, adc Janna, support Swain, jungle Swain, jungle Leona, adc Lulu, adc Zilean, ....

Winning against bad players doesn't make something good, it just reinforces the badness. ADC Gnar doesn't work against half competent players post lane phase because he gets blow up in two seconds and has really terrible range, not to mention the last thing you want on an ADC is to suddenly to go melee with it.

out of 6 games

Honestly I'm on the side of the writer of the guide here. contrary to you guys I've actually tried adc gnar, and I won every game I played