Without commenting on the specifics of this particular post (God-willing, I'll find the time to do a proper critique of the edits and post it as a separate answer), I'll throw in my two cents on the general editing of answers (community wiki notwithstanding).
First, for context, I quote the following from the help centre:
When should I edit posts?
Any time you feel you can make the post better, and are inclined to do
so. Editing is encouraged!
Some common reasons to edit are:
- to fix grammatical or spelling mistakes
- to clarify the meaning of a post without changing it
- to correct minor mistakes or add addendums / updates as the post ages
- to add related resources or hyperlinks
The second point here is, I feel, the most important: To clarify the meaning of a post without changing it.
Voting on answers is of vital importance to this site. Not only does it reflect the actual expertise of the poster, but it reflects how useful they are to the community as a whole and by extension what powers they have to actually moderate the community.
If an edit to an answer substantially changes it, this system destabilizes. If, for example, the edited post demonstrates expertise that the original poster doesn't likely possess, the votes no longer reflect that; such post-edit votes would typically apply to the user who edited the post, but they're given to the original poster instead. Similarly, since there's no real way to distinguish pre-edit and post-edit votes, the score on the post no longer accurately reflects either; you'll very possibly just end up with a good post having a lower score than it deserves thanks to pre-edit voting.
This not only risks presenting the original poster as an expert (or non-expert) in a field incorrectly, but it also unfairly prevents the expertise of the editor from being reflected.
And if there is a fundamental problem with the post that renders it useless (such as it not actually answering the question, being pretty much unintelligible, or even being outright wrong), again editing is not the tool for fixing that. As above, editing such posts to make them useful incorrectly allows post-edit votes to present the original poster (rather than the editor) as more useful than he actually is; this can be highly problematic for the purposes of site-curation since user reputation is directly correlated to how much power that user has over the site.
The Stack Exchange model is built around the very concept of giving experts, useful experts, the tools and ability to moderate themselves, and editing should be done with this idea in mind: You're not trying to make the poster appear more (or less) expert, or more (or less) useful to the site, you're trying to clarify the poster's actual expertise and usefulness.
The difference between things like "fixing minor mistakes" vs "correcting a technically wrong answer", or "adding addendums/updates" vs "introducing new expertise" can be a bit of a judgement call, but it's usually fairly obvious to other users with domain expertise what a poster actually intended, or would've actually included had the facts been brought to their timely attention. Other experts are often the best judge of expertise and usefulness, and as such are often the best judge of what actually reflects that expertise and usefulness.
And if you find yourself wanting to make an edit that actually changes an existing answer on a fundamental level, chances are what you really want to do is just post a new answer instead.