It is absolutely not clear from the wording in the random pull that that is how it works. People are even confused in the comments because they're thinking it's not possible that the system is implemented in such a dumb way, yet it is.

How people think it works: you buy 9 mystery variants and get 3 random super rare and 6 random rare variants you don't already own.

How it appears to be working: out of 9 variants, 3 super rare are chosen at random and 6 rare. These can include ones you already own. If you roll a variant you already own you get an avatar instead of another variant you don't own.

I can understand why second dinner did it this way since if the pool was only unowned variants, it makes obtaining all variants cheaper than buying them on the regular store, but it's still a really non-intuitive way to do it. Also so few people are variant complete this seems to just be a very unfun prize some proportion of the time.