Discriminators are important! Here's why

Here are the reasons the blog post states that discriminators are being removed:

• The devs perceive them as complex.
• People don't know that it's called a discriminator.
• People don't remember what their number is.
• There are more than 9999 Mikes, Janes, etc.

Reason 1 has some merit. Because at a glance, it does add complexity. But in practice, it actually reduces complexity. Just as you know that a phone number is almost always 10 digits, you know that a Discord handle always ends in 4 numbers.
The mental load of remembering e.g. "thirty-eight seventy-three" in addition to a username is less than having to remember whatever mutations someone added because their handle was already taken (e.g. "It's John Doe, but with the o replaced with 0, but only the first, not the second, and also there's a hyphen between my first and last name").

Reasons 2 is moot. I can still use something without knowing what it's called. If need be you can just call it "the number" and people can infer what you mean from context.

Reason 3 is also moot. I also don't need to remember the number when I have it right there at all times. I don't remember my phone number either, because it's in my phone, and I carry my phone on me. That doesn't mean phone numbers are fundamentally flawed.

Reason 4 is also moot. Mike number 10000 is not going to be able to get the handle "Mike" even if discriminators are removed. However, 9998 Mikes are going to lose the handle "Mike" going forward. Probably more, with case-sensitivity being removed.
It's better to be unequally fair than to be equally unfair. I.e. it's better to only allow 9998 duplicates of a taken handle than no duplicates at all.

This leaves only reason 1 as having any amount of merit at all, and the amount of merit it has is dubious at best and remains unproven.

Now, here are some reasons why discriminators are important and should never even have been considered for removal in any form:

• Normalization: as mentioned before, you always know exactly where the numbers in a Discord handle are and how many of them there are. This gives them a certain amount of uniformity, which is a good thing.
  If someone tells you their email is "john_doe" you know you still need to ask for their email provider. If someone tells you their Discord handle is "john_doe" you know you still need to ask for their discriminator (even if you don't remember what it's called!)
• No handle sniping: if you've got a particular handle you're known by on multiple social media platforms, it's annoying if your handle is already taken when you're signing up. This problem gets even worse if you're someone noteworthy, in which case the handle is almost certainly already taken.
  If you know someone on other social media platforms, and you want to add them on Discord, ideally all they'll have to tell you is the discriminator. Since the name part of the handle is non-unique, they can set their name to be identical even if multiple users with that name already exist.
• No undue authority from "clean" handles: someone with a handle like "John_Doe" is always going to seem more trustworthy than someone with a handle like "John_Doe17", even if the latter happens to be the John Doe, the one everyone knows about. This is not the case when all John_Does have 4 numbers behind their name, since you know that the discriminator is more like an address than an identity.
• Preventing impersonation: in tandem with the above, removing discriminators makes it astronomically more likely that people will  be able to impersonate public figures or companies that do not as of yet have a Discord presence. It also encourages people of note to sign up for Discord only to never use it, just so people can't use "their" handle. Neither of these is good for the overall health of the Discord community.
  It's a lot harder to fool someone into thinking you're someone important because of your handle, when it's immediately obvious that up to 9999 people could have that particular handle.
• Greater control over identity: even if you give someone a display name they can freely mess around with, their username is still a key part of their identity. By requiring that everyone's username is unique, you would be arbitrarily restricting their ability to express themselves. If you think people will no longer care about their username once the display name exists, you're very wrong.
• Easier to remember: it actually helps to make handles easier to remember. It's a hybrid approach that's the best of both worlds. A non-unique user handle with a 4-digit number to disambiguate it is easier to remember than a user handle that's got arbitrary changes made to it in order to be unique, and it's a lot easier to remember than e.g. a 16-digit number.
  The name part provides the identity, and already removes most of the ambiguity by itself. The 4 digits at the end remove the rest, and since they're required, they don't dilute the identity.
  To borrow an example, if the name part of the handle can be something like "vernacular", that's easy to write and easy to remember. But if it must be unique, the moment more than one person wants to use that handle you're going to get unintuitive variations. With the discriminator, you know exactly what form the variation will take, and you know for sure that it'll be there.
  When names need to be unique, on one platform this person might be known as "vernacu1ar". But then that one is taken as well on another site, and you get "vemacu1ar" or "vernacular_42". There's no way to predict which handles are free and which aren't. This is a major frustration with picking handles on basically every platform that doesn't use discriminators.
• Larger supply of usernames: some usernames are in demand. If they all need to be unique, usernames might end up being sold and bought because they have prestige attached to them. Owning a really neat handle when there's only 1 of them is a big deal. It's not such a big deal when there are 9999 of them. So discriminators discourage people from taking (or even hoarding) important or cool usernames.

In a void, it's easy to say "these numbers at the end are doing nothing", but things in the real world don't operate in a void, and those numbers are doing a lot of heavy lifting.

Lastly, I'd like to call back to reason #4 for removing discriminators again, which is the complaints from Mikes and Janes. I don't understand how this is supposedly a reason to remove discriminators. It's one of the strongest reasons to keep them.
It's the lack of complaints from people who use less common names when compared to the Mikes and Janes that show just how well the system is working. The fact that the amount of complaints you get from the Mikes and Janes is noteworthy at all means that this feature is preventing a lot more headaches than it's causing.