I, and several other reviewers, have repeatedly rejected this edit. It's ungrammatical (easier is an adjective; it can't modify legible, another adjective; it needs an adverb, like "more easily" instead). It makes the post worse. If an account proposed this edit, the account would lose edit privileges. But it's not proposed by an account. An anonymous user proposes it.
It seems like there should be some way to permanently reject the edit, rather than allow it to be proposed repeatedly.
We're aware of the situation and are monitoring it. Good news first: that particular user won't be bothering us for a while. At least not from that IP address, but I know for a fact they've used multiple IP addresses in the past. We've taken out their IP addresses.
Anonymous users are very hard to moderate and some of their actions can indeed be a nuisance. There are a couple of approaches possible, none of them great.
rene's answer details one of them: a spam/vandalism flag on a suggested edit. This is the right tool if the edit is destructive, it's the wrong tool for poor edits. However, considering the limited tools we have, some consider it an acceptable tool versus anonymous users. While we're investigating the possibilities, no review suspensions will be handed out for using this option on anonymous users. Please stick to the proper tools with registered users. Even if it would've been the correct tool, if the goal is to take-out repeat offenders with this you'd have to know it's a repeat offender at the time of rejecting. Collaborating about the moderation of the site in chat has been done with great effect in the past in The 2nd Monitor, don't hesitate to do it again. If need be, new rooms can be started. They're free-of-charge.
If the edits are truly nonsense and the user has no other participation of value on the site, the user can be destroyed. Destroying a user for spam will feed their IP into SpamRam and has the benefit that it can be done years after the fact. Doing this for poor edits is still not the right approach, but can be an option for repeat offenders without contributions of value.
Another approach is to limit the action of all unregistered users. Sites can petition the staff to limit the privileges to disallow answers, disallow suggested-edits, etc. It's actually fairly easy to get implemented and has been used with great success to stop unscrupulous actors in the past on other Stack Exchange sites. However, we're not going to take this approach unless there's support for it from the community. It's not a nuclear option, but it comes close. Personally I'm in favour (the amount of garbage edits we get from anonymous users is percentage-wise high and the amount of effort it takes to create an account is small) but this is still not an autocracy. If you think there would be enough people in favour, feel free to start a meta question suggesting it. In an emergency situation, we could temporarily instate this somewhat rapidly.
Rejecting a specific edit permanently is not an option enabled by the system, nor would it be a viable approach. I'd very much like the option to disable suggest-edit privileges per IP like we can do per user, but AFAIK there's no support for that by the system.
I'll address the repeatedly aspect of your question. This suggestion will not work for one-off incidents or after the fact.
Stack Exchange has functionality in place to block spam and/or abusive content coming from the same source. It exact workings are secret but it is known as SpamRam. Regular users and mods have a few ways to indirectly interact with SpamRam. One most noticeable is raising a Spam flag on a post. After 6 spam or R/A flags the IP address of the original poster is put into SpamRam, effectively blocking them from accessing the network from that IP address. The block expires after a while but repeat offenders will see longer block times going forward.
While reviewing a suggested edit reviewers can choose the first option in the reject dialog:
Spam or vandalism
This edit defaces the post in order to promote a product or service, or is deliberately destructive.
when two reviewers pick that option, not only did you stop that edit from going through, you also added the IP address of the user behind that edit into SpamRam.
So if you have a case where a single entity is repeatedly suggesting harmful edits and these edits are easily recognizable you could organize a rejection mob in a chatroom and instruct the reviewers for these kinds of edits to pick the Spam or Vandalism reject reason, effectively blocking more of such edits coming in in the short term.
Before you consider this route do consult, involve and obtain permission from your site moderators as, in general, chatrooms with organized moderation power tend to spiral out-of-control when not governed correctly.
I just wanted to point out that I believe that there was one aspect of this that took it from simple bad editing to active vandalism: it was repeated. It's one thing to make a bad edit. That can happen to anyone. But even after being rejected multiple times, making the same identical edit is not kosher.
For that reason, I think that in this particular case, it was appropriate to mark it as vandalism. To my mind, the only reason that anonymous mattered at all is that it allowed for repeated edit attempts, where the system already handles repeated bad edit attempts by a registered user.
I do not see this solution as generally appropriate for bad edits by anonymous users. I do see it as an option in cases similar to this one, where the same edit is attempted repeatedly. Or where similar bad edits are made to multiple posts.
