If the stain of our sins is what leads us to purgatory, and prayer, fasting, confession, mortifications and suffering removes those stains, I’d think many Saints went straight to Heaven. I think the extreme sufferings they endured, as well as their pious prayerful lives would have gained them immediate entry into Heaven. Our sufferings on earth can serve as our purgatory (from what I understand).
If anyone has ever gained immediate entry, it would be the saints who gave their lives to God- the ones who lived their lives completely for the conversion and salvation of souls. I think this would also apply to anyone who has died as a martyr for their faith.
It’s an interesting topic- makes me think of the incorruptibles. Saint Catherine is incorruptible to this day- except for a small spot around her mouth. She was prone to vanity as she had bad teeth and frequently covered her mouth when laughing to hide them. Although her body hasn’t decomposed, God allowed a small amount of decomposition around her mouth to point it out. I’d think her life would still have allowed her to gain immediate entry- but I guess we won’t know until we get there…