I consider Roberts a liberal for a case like this so I think the court is 5-4 now and if Breyer doesn’t retire before 2022 (when Republicans are 99% likely to take the Senate) it will be 5-3 until there’s a Republican President.
If you classify Roberts a liberal, then your math makes sense. Roberts might not be as far right as some, but there is no way he could ever be classified as a liberal court member.
