It does seem like they're mistaking two issues as one. Because you can't submit a friend request without knowing the descriminator I don't see how it would be involved in failed friend requests, I would put the blame for that squarely on case sensitivity. And not knowing your descriminator isn't really a problem, it's shown prominently on your UI if you need it, it's not as though the unique user names people come up with will not be similarly prone to forgetting when it has no use outside of friend requests.
I don't know a single one of my friend's phone numbers. I give my phone to them and they type it in. It has never been a problem. It's not just me, literally no human being has ever had a problem figuring out how to send their friend a SMS message.
I have no idea what Discord is up to. They made a big decision in a weird meeting.
My guess is that they look at application analytics what features are used and how often and see that in 40% of cases the send friend request form is not being submitted and just closed.
