Quick answer
What to do first
Roll for a role your base is missing, then test one upgrade against the same wave instead of chasing an unsupported rarity claim.
A safe approach to build a base rng best upgrades starts with coverage, not a guessed odds table. Identify whether the base lacks an entry, middle, or cleanup role; roll or upgrade toward that need; preserve the rest of the layout; then replay one comparable run. Record the first failure before and after the change. Exact roll chances, pity behavior, upgrade prices, and a universal “best” path are intentionally omitted because they are not available from a current authoritative source.