Personally i think Naruto came quite far,and i myself didn't expect it to lose against Gintama actually while i do like Gintama more i had thought after Naruto beat Berserk and Tokyo Ghoul it wouldn't fall against any Manga till the Semifinals actually.
With Fairy Tail i wouldn't be so sure actually,it was facing One Piece which has a huge Fanbase here on MH and furthermore was dragged down by it's not so great Ending/Conclusion of the War of which i personally think that it surely had an Influence on People's Decision in that Match.
And i honestly think that the Campaigning did play a fair part in that but yeah that's just me,the campaigning is first and foremost for the by you mentioned Reason imo. Which would be to try and influence some People's Decision on who to vote for in case they are struggling between 2 Series that they like to an Equal Amount.
I view these "Wars" more as a Matter of Preference actually,during all the Previous Rounds i mostly voted for the Manga that i liked more if i was conflicted on who to vote for i left it to the Nominators and their Campaigns.
Just my Opinion.
I thought somewhat along the lines of BluePegasus at first (on account of never participating in any “wars” before) but soon learned not to take this as a “let’s decide which is better”. It’s more of a “let each fan base bring whatever artillery they’ve got to the battlefield”. A lot of people here think of it as just a fun event and enjoy the campaigning, deal-making and backstabbing of it more than the actual debating, I think, and will vote against superior manga for silly reasons just as well as well-made points about the quality of the manga.
Throughout the event I’ve learned to think a little more like these people, but I get where Pegasus is coming from.