These two are the big outstanding ones, SC for rarity (have yet to see one personally) and OP for the sheer quantity required.
The only thing that comes a little close are Settlement Defense Plans. It's a rare find, which is fine, but is being let down by requiring 15 of them. I thought the patch notes would have fixed that by matching the dialogue which mentioned 5, but it was fixed the other way around.
This is post-collection feedback, I have gone through these unlocks myself, so any easing isn't going to change anything for me, but I do believe that it's going to cause a fair bit of resent in the greater community if left as is.
On the positive side, I started giving away my extra random drops to other players, so maybe that's how those unlocks will go over time, with a community handing out those precious-but-only-once items to players who need them. But being handed out the stuff isn't going to feel the same.