I can't speak for the others, but I myself make a lot of mistakes in my English, and, as a rule, CocoPop's edits make my posts look better to me than they did before those edits.
Sometimes they don't, in which case I just revert or edit them.
I can't speak about his motivation, but, fwiw, editing others' posts does not affect the editor's reputation beyond a certain point (which he has long since reached).
We cannot ban someone from editing posts just because the original author doesn't like the edits. A user can be temporarily banned from editing by the system if lots of their edit suggestions are rejected, but it only works for low-reputation users whose edits go to the review queue.
I can see that in the case you have mentioned his edits were not justified. It happens. It has happened to me too. It took me less than ten minutes to roll back or edit those edits and explain the reason why I did it. In every single one of those cases I could see that I myself was not clear in the first place.
The fact that a native English speaker, whose command of the language was for the most part something he developed effortlessly as a child, is correcting English mistakes made by me, who had to go through the effort of learning it as an adult, does not hurt my pride. I've been getting it all my life from my blog visitors, book editors, Stack Overflow commenters and lots of other people. But I can see it how it can hurt someone else's.
This is, unfortunately, something that is bound to happen on any community edited website. This issue has been raised countless number of times in moderatorial discussions, and the consensus remains the same: we try to urge the editors to be sensitive, but, unless they are really rude or condescending in their edits or remarks, we don't stop them.
While unsolicited correction of others' language, especially one which adds nothing to the meaning the speaker intends to convey, would indeed be rude and condescending in spoken communication, we don't consider it as such in written posts that are intended to be read and re-read by, hopefully, the generations to come.
Whatever vile and disgraceful motives the editor has in their mind when, with a spiteful cackle, they put a missing "the" back where it belongs, we don't stop them from doing it. If they, inevitably, make disruptive edits every now and then, the course of action would be to fix those edits or roll them back. Unless the burden of doing so every once in a while exceeds a certain threshold (which, at the time of this writing, is not anywhere close) we won't be taking any administrative measures.
The site is designed in such a way that its entry page features questions which recently saw some activity. I don't have any more say than any other participant in the matters of site mechanics, and the creators of the site seem to want it this way.
If someone decides to spend their time providing meaningful edits, however small, which has as a side effect, intended or otherwise, old posts floating up and the front page being replete with their nickname, then it will happen.
As long as most of these edits are beneficial, albeit small — which I think CocoPop's are — I'm not inclined to limit them using my moderatorial authority or otherwise, even his actions are driven by some hidden agenda, whatever it might be.
Of course, if the mass of user's edits turned out to be demonstrably disruptive to the site, even if each and every one of them in isolation would seem innocuous, that would make grounds for administrative action. However, so far I'm not seeing any signs of this happening.
The only way to effect change in the appearance of the front page, which would align with the design goals of the site, is contributing meaningful, beneficial edits, answers, or questions of your own — an endeavor that I encourage in every way.