Hello @developers,
I understand what you’re saying here, but unfortunately I don’t think we have a clean solution to this…
At first I thought “maybe you can limit it with permissions… what if you let them create new Multi Table records but not view them?”
Hey, waddya know… that made the “From Library” button disappear!
But… this is actually broken
If they try to create a new record…
They can edit it and click save, but then they get this error:
Because, well, we explicitly told the permissions system they cannot view any records… not even the one they just created 
So that won’t fly. (The field error is a separate bug that I’ll report, but even if we fixed that, it still wouldn’t work the way you need it to.)
And even if we could just hide the button somehow without affecting their permissions, well, they’d still be able to use the drop-down menu to simply choose a record:
I think overall, trying to do it this way would be deliberately fighting the system design, and it’s going to cause you trouble at every turn 
It’s ultimately a lifecycle thing, and there’s no easy way to change that… a Link is ultimately, as you say, a reference to:
a record that is used in multiple places
We cannot change that fundamental behavior without breaking a lot of other systems. Even if we prohibited them from being able to link to existing records in the UI, that limitation means that if they ever accidentally un-linked the record in that field, they’d have to re-create it from scratch. And then you’d end up with a bunch of duplicate and orphaned records…
So we’d have to have a system that says "this record can only link to new records, not existing ones, and then once created, that linked record cannot be linked from anywhere else and cannot be independently destroyed "… which sounds, well, a lot like a block 
A block IS the system’s intended solution to this scenario, by tightly coupling those fields to the to parent record. The block doesn’t have its own lifecycle outside of that record, and cannot be referenced by other records.
I don’t know that there is any easy workaround to fixing that inherent difference in these systems’ intents…
However… is there anything we can at least try to improve from the UI side to make blocks easier for your editors to use in this configuration?
Like:
That is a very interesting suggestion, the ability to open a block (or a fieldset, prehaps) in a separate modal for clarity and ease of editing. If we focused the suggestion on that aspect, could that be sufficient for your editors?
(And you already do have some limited versions of this, like being able to at least open text and structured text fields in a popup modal)
I hope this doesn’t come across as argumentative. It’s just that record relationships are such a fundamental part of the current system design that drastically changing their behavior to accommodate this particular use case would probably be quite difficult and cause all sorts of unintended consequences — especially when blocks already exist and are already designed for this use case. If we could make blocks better, instead of overhauling how record relationships work, would that be good enough? What do you think?