While there is some merit to the idea on a really fast moving site like SO, here on SF we're slow enough that for most questions the long tail pays better than the immediate post. There are questions here where there will be three answers on it within two minutes of posting, which is the exact case you're talking about here.
However, in my experience these questions are a small minority of questions that arrive on SF. We actually get more 'does not belong here' questions than we do the sorts of questions where fastest-gun is a big problem. What's more, many of the fastest-gun questions are actually duplicates of other historical fastest-gun questions so dropping a book-sized answer is not that productive.
There are some competing interests when it comes to questions, answers, and voting:
- The questioner just wants their question answered. Faster good-enough questions may be all they need or want.
- The answerer wants the accolade of their peers (votes). They want each question given equal consideration by voters.
- The electorate hates stupidity and wrongness. They'll upvote the good stuff and occasionally downvote the bad stuff in order to drown out the bad stuff.
- The long tail just wants the best answer. They'll upvote the good stuff for years after the questioner has wandered off.
Point 1: The Questioner
There is a reason that some low rep users have a waiting period between when they ask a question and when it can be marked accepted. This is so they don't post a question, come back five minutes later, read the three answers, accept one, and leave. It's to incentivise answerers to keep working.
Secondly, getting answers is the whole point of these sites. Many, many users will just wander away if their question doesn't get any attention within 10 minutes of posting. A steady stream of answers is a good thing. Fast upvotes tell questioners which answers are the good ones. Feedback is good, since it encourages repeat visits.
Point 2: The Answerers
Answerers want votes and accepted checkmarks. Accepted checkmarks are great since they bring a low-voted answer to the top of the list for the long tail to consider and vote on. Does each question get an equal weighing by voters? No, in most cases the top three vote-getters are all that are read.
Point 3: The Electorate
There are fewer of these around than there used to be, but there are SF users who read questions so they can vote on them. You can tell who they are by looking at the Electorate and Vox Populi badges. For the rest, they'll read questions for which they have sufficient clue to possibly drop an answer on it and end up voting for the answers that are already there.
Want an easy way to encourage voting on question? Drop a slightly wrong answer on it. It'll cause voters to upvote the others, and occasionally downvote the bad one. If there is one thing our electorate hates, it's seeing crap have equal weight with a good answer.
Point 4: The Long Tail
Questions earn rep long after the OP has left the site. I've earned many Enlightened or Good Answer badges from questions over a year old. A couple of my answers have earned more than the accepted answer on a question.
When answering questions, even fastest-gun style questions, remember you're answering for Google as much as you're answering for the questioner. If you do a good enough job of answering, it might even make it onto the canonical answers list and used as a Duplicate-Of close-target; which will earn rep over the long tail.
Your proposal overbalances in favor of Answerers. They are the bulk of our active community, but StackExchange as a whole has deliberately tipped things in favor of questioners and the long tail in this regard.