There is one really important thing you have to remember about Area 51:
A proposal is not a site.
In other words, don't panic.
I've been very light with applying [closed as duplicate]. And that has been very deliberate.
I look at proposals and often feel as you do: "ugh, this is just a subset of [other proposal]." So, what do you do? How do you know the 2nd proposal isn't the better option? There's nothing inherently correct about being first. So, I leave it and watch. A proposal is not a site.
For the most part, ill-conceived or ill-defined proposals—even proposals that seem just somehow off—aren't getting support.1
In short, Area 51 is working exactly as designed. Taking the approach of "ignore it and move on" is an option. State your concerns in a comment, if you must, and throw your support to more interesting proposals. In almost every case I have seen so far, there is nothing to "handle."
But there will be a time where two competing proposals have such a groundswell of support that both have sufficient momentum to sail through. That is the time to look closely at the two proposals. Are they different enough to justify separate sites? Or is the demand so high that, even after accidentally splitting the audience, each side still has sufficient support. In those cases, we'll have to step in and merge the proposals for their own good.
There's no use in worrying about it before then. Ignore proposals you are not interested in.
1Yes, there a bunch of proposals not getting support because the audience isn't there, yet. I'm not talking about you.