Doubt that they changed the droprates in the last year+. It is just RNG being RNG.
That said: What exactly is the illusion you seek for? Because I am pretty sure that not a single DLC illusion (weapons, cosmetics, anything) can be acquired through chests.
I saw a comment or thread on these forums saying it might be a good idea to add the pseudo chance they did to crits to chests. I actually don’t know how to feel about it. I think it’s good to have a new discussion about it. As this could potentially fix some issues players have with red items and illusions overall (also no dupe illusions).
Added pseudo random distribution to critical strikes and procs.
What this means is that everytime you attack and don’t trigger a critical strike, the chance of you triggering a critical strike increases slightly. This should help flatten the bell curve slightly when it comes to large periods of either no critical strikes happening, or all critical strikes triggering in a row.
I think red drop chance should has like this thing too.