Solution: Disable voting on the top comment(s). This would allow the trailing comments to catch up until they are the top comments and their voting is disabled. The top comment can't race far ahead of the others.
But this would still result in the topmost comments getting most upvotes — all topmost comments except for number 1?
Now I'm oversimplifying, but the effect would be that comment 1 and 2 swapped place over and over again. Or the first N + 1 comments, if you restrict voting on the first N comments. (And people might be confused, perhaps annoyed, when they cannot vote on the first N comments?)
This would not help promoting [a really good but forgotten comment] that is located far away at position 10 or 20.
Perhaps a slight modification: the farther down the list, the more an upvote should count (because of the top-comment bias), with it being unnecessary all together for the current winner... If someone is up-voting a comment farther down, they not only went to the effort to scroll, and they should be rewarded for actively curating, but it means they had to endure other comments higher up that were not as worthy, which is an increasing burden the further down the comment was found (for example, a geometric weighting of upvotes). It might mean more flapping of the position, but it also ensures equal (fair) exposure of equally-good comments.
The submission ranking, I assume, takes more into account than just upvotes (age, number and quality of sub-comments, etc). The top-comment problem feels like the same problem, so might be an opportunity for code consolidation.
Solution: Disable voting on the top comment(s). This would allow the trailing comments to catch up until they are the top comments and their voting is disabled. The top comment can't race far ahead of the others.