Remove Collected/Not Collected from the Collection filter and add an option for "0" into the current number collected list.
Currently, the "Collection" filter contains:
Collected | Not Collected
x1 | x2 | x3 | x4
This ends up being confusing, as the Collected/Not Collected options don't interact well with the "number collected" values. I I click "Not Collected" and, for example "x4", this filters out all of the collection as the "Not Collected" option is only showing the cards there are zero copies of, while the x4 filter only shows the cards you have a playset of. The two filters cancel each other out.
It would be much more intuitive to remove the Collected/Not Collected and change it so the number of cards can be selected in a range 0-4 inclusive. If the player only wants to see "Not collected" cards, they can select the 0 option only.
The major advantage of this, other than being far more intuitive than the current system, is that a search of "what do I not have a playset of?" is now possible. Currently, there is no way to show "cards that I own 0, 1, 2 or 3 of", yet this is the most common search I want to perform to see what I need to complete a collection.
With this change, I would also recommend displaying uncollected cards by default.
Note this idea could also be tweaked by only adding the 0 option to the number of cards collected list (although the change does make the Collected/Not Collected checkboxes redundant)