Wa alaikum salaam,
One's rank with Allah Most High is veiled from us. The Messenger of Allah ﷺ said, "Verily Allah does not look at your forms or your bodies; rather He looks at your hearts and your intentions." Now, as a general point of belief, the scholars have agreed upon the fact that one's faith increases and decreases, in accordance to their sins and good deeds.
When we discuss a term, such as 'Major sinner', we must understand that this is but a legal ruling ascribe to someone who commited an outward major sin. Such a person is considered to have done actions contrary to the dictates of their faith. Linguistically, you could call such a person a hypocrite. However, hypocrite is of two types: one who acts contrary to what they claim and the other, on who believes contrary to what they claim.
The first type of hypocrite is still a believer but a sinful one.
The second type is a disbeliever as they profess faith in Islam publicly - whilst concealing disbelief in their hearts.
Both types of hypocrites are described throughout the Qur'an. However as we mentioned in the beginning - major sinner is a legal classification based on outward legal rulings. Allah Most High, however, knows the apparents and the concealed; He knows what is in one's heart regardless of their showing it publicly.
Righteousness and Transgression are qualities of the heart first and foremost. Thus a person involved in an outward major sin - such as drinking wine - however, they are filled with remorse, humilty, reverance, and pentance with Allah Most High - such a person is closer to righteousness than many of those who don't commit such aggriegious sins.
Hope this helps
Feel free to ask any follow up questions