“On the other hand, some people are holier than others.”
No they are not. All believers are holy because of His holiness. Mary is no more holy now than the newest believer who has entrusted herself to Christ just moments ago.
Mary does share one blessing with all who are now in the presence of the Lord - no more sin nature.
Matthew 5:19
"Therefore anyone who sets aside one of the least of these commands and teaches others accordingly will be called least in the kingdom of heaven, but whoever practices and teaches these commands will be called great in the kingdom of heaven."
Matthew 11:11
"Truly I tell you, among those born of women there has not risen anyone greater than John the Baptist; yet whoever is least in the kingdom of heaven is greater than he."
If everything and everybody were, by necessity, equal, then it would be impossible to speak of "growing" in grace. We grow because we CAN grow; because God can cause this increase in us; there IS such a thing as greater or lesser grace.
2 Peter 3:18
"But grow in the grace and knowledge of our Lord and Savior Jesus Christ. To him be glory both now and forever! Amen."