On Matthean priority, Mark and Luke simplify the narratives. Some errantists would quibble that in doing so they introduce factual errors, suggesting that one person was present rather than two, but I wouldn’t want to press that point too far.

On Markan priority, Matthew embellishes the narratives. I’m still trying to find a good explanation of why he might do so.

Since I already agree with the earliest church historians and accept Matthean priority, I’m not going to change that view now. As such, my view is that Mark and Luke removed a demoniac for narrative purposes (though that still doesn’t sit well with my inerrantism). They similarly removed a blind man for narrative purposes.

What are these narrative purposes?

In all cases, an account with one miracle of a certain type is simpler to relate than an account with two or three of that type, especially if you want to make the story more powerful by elaborating on the details of the subjects of the miracles (the demoniacs and the blind men). These details of individual lives are likely to diverge and complicate the story. For example, perhaps only one of the demoniacs cut himself with stones. Perhaps the other suffered in other ways. Perhaps only one demoniac had ever been put in chains. Clearly, only one of the blind men was named Bartimaeus, etc. One subject is easier to profile than two or three.

In the case of the demoniac, it may also be that Mark and Luke are only telling the story of the demoniac who wanted to follow Jesus after the exorcism. They both mention the fact that the freed demoniac tried to follow him. The other demoniac did something else and Mark and Luke chose not to tell his story for that reason. Matthew simplified his account in a different way by leaving out how either demonic suffered before or responded after his liberation.

In the case of the blind men near Jericho, Luke is only telling the story of the first blind man healed. But Mark is only telling the story of the blind man who became known by name to the early believers (or perhaps the story of the only one whose name Peter ever learned). Even Matthew simplifies his account by leaving out at least one blind man: the one healed on the way into the city.

In any case, this is all a long-winded way of saying that because I don’t accept your premise that Matthew added a demoniac, I don’t feel any particular pressure to assume that he added a blind man near Jericho.

I agree with the point that blind beggars by the road are more common than demoniacs among the tombs, and that saying that Matthew is recounting a different incident is therefore more plausible in the blind beggars case than it is in the demoniacs among the tombs case. (N.B. Saying that it’s “more plausible” falls short of saying that it’s “plausible”.)

However, the fact that elsewhere Matthew seems to have taken an account with one demoniac and added a second makes me think that he may well have done a similar thing here, taking an account with one blind beggar and adding a second. He’s got form.

For that reason, I’d be most comfortable with a harmonisation that treats all of the accounts as accounts of the same event, if such can be found.

You might argue that the similarity of the words used in each case make it likely that the same event is being recounted. The blind man, for example, always cries to the Son of David to have mercy and the crowd initially tries to silence him.

But a single-healing hypothesis is not the only explanation for the similarity of the accounts. For starters, whatever reasons the crowd had for trying to silence the blind men, be there 1, 2 or 22, apply in each case. I suppose that the most obvious reason the crowd had to silence the blind man was that they were trying to hear Christ speak and the caterwauling blind man was preventing that.

But what about the similarity of the words of the blind men themselves?

One might argue thus:

1. Jesus heals the first blind man, per Luke, on the way in to Jericho.
2. Word of this miracle gets around.
3. As a result, by the time Jesus leaves the city a second and later a a third blind man appeals to Jesus for healing.
4. Just to be sure, the two later blind men use the same words that had ‘worked’ for the first blind man.

One of these later blind men, Bartimaeus, became well enough known to later believers that Mark tells his story and mentions him by name. But just as he did not mention the the healing on the way into the city, Mark does not mention one of the healings on the way out of the city.