The major sins

[azc]

1. Associating anything with Allah
2. Showing disrespect to parents
3. Murder
4. Practicing magic
5. Abandoning salah
6. Not paying zakah
7. Not fasting during the month of Ramadan without excuse
8. Not performing Hajj, while being able to do so
9. Severing relations with relatives
10. Committing adultery
11. Committing sodomy
12. Dealing in riba (interest)
13. Wrongfully consuming the property of an orphan
14. Lying about Allah or His Messenger
15. Running away from the battlefield
16. Deceiving the people that one rules and being unjust to them
17. Being proud and arrogant
18. Bearing false witness
19. Drinking alcohol
20. Gambling
21. Falsely accusing chaste women (i.e. of committing fornication or adultery)
22. Stealing from the spoils of war
23. Stealing
24. Committing highway robbery
25. Making false oath
26. Committing oppression
27. Earning ill-gotten gain.
28. Consuming what is unlawful.
29. Committing suicide
30. Lying frequently
31. Judging unjustly
32. Giving and accepting a bribe
33. Imitating the opposite sex (in dress, behavior, and the like)
34. Allowing one’s wife, daughters, etc. to display their beauty to men or conduct illicit sexual relations
35. Marrying a divorced woman in order to make her lawful for her ex-husband to remarry her after he irrevocably divorced her
36. Not protecting oneself or one's clothes from being contaminated with urine or excrement.
37. Showing off
38. Learning knowledge of the religion for the sake of this world and withholding that knowledge (i.e., not teaching people)
39. Betraying a trust
40. Recounting favors
41. Denying Allah's Decree
42. Listening to people's private conversations
43. Carrying gossip
44. Swearing
45. Breaking contracts
46. Believing in fortune-tellers
47. Behaving badly towards one’s husband
48. Making statues
49. Lamenting, wailing, tearing the clothing, and doing other things of this sort when an affliction falls
50. Treating others wrongfully
51. Treating one’s wife, servant, the weak, and animals badly
52. Offending one's neighbor
53. Offending and abusing Muslims
54. Offending people and having an arrogant attitude toward them
55. Trailing one's garment in pride
56. Wearing silk and gold (this is for men only)
57. Running away from one’s master (this is for slaves)
58. Slaughtering an animal that has been dedicated to anyone other than Allah
59. To knowingly ascribe one's paternity to a man other than one's biological father
60. Arguing and disputing violently
61. Withholding excess water
62. Giving short weight or measure
63. Feeling secure from Allah's Plan
64. Offending pious people
65. Not praying in congregation but praying alone without an excuse
66. Persistently missing Friday Prayer without any excuse
67. Usurping the rights of the heir through bequests (to others)
68. Deceiving and plotting evil
69. Spying for the enemy of the Muslims against Muslim's interest
70. Cursing or insulting any of the Companions of the Prophet

Source:The Major Sins(Al-Kaba’ir) by Muhammad ibn `Uthman Adh-Dhahabi

[Nitro Zeus]

1. Associating anything with Allah
2. Showing disrespect to parents
3. Murder
4. Practicing magic
5. Abandoningsalah(ritual Prayer)
6. Not paying zakah
7. Not fasting during the month of Ramadan without excuse
8. Not performing Hajj, while being able to do so
9. Severing relations with relatives
10. Committing adultery
11. Committing sodomy
12. Dealing inriba(interest)
13. Wrongfully consuming the property of an orphan
14. Lying about Allah or His Messenger
15. Running away from the battlefield
16. Deceiving the people that one rules and being unjust to them
17. Being proud and arrogant
18. Bearing false witness
19. Drinking alcohol
20. Gambling
21. Falsely accusing chaste women (i.e. of committing fornication or adultery)
22. Stealing from the spoils of war
23. Stealing
24. Committing highway robbery
25. Making false oath
26. Committing oppression
27. Earning ill-gotten gain.
28. Consuming what is unlawful.
29. Committing suicide
30. Lying frequently
31. Judging unjustly
32. Giving and accepting a bribe
33. Imitating the opposite sex (in dress, behavior, and the like)
34. Allowing one’s wife, daughters, etc. to display their beauty to men or conduct illicit sexual relations
35. Marrying a divorced woman in order to make her lawful for her ex-husband to remarry her after he irrevocably divorced her
36. Not protecting oneself or one's clothes from being contaminated with urine or excrement.
37. Showing off
38. Learning knowledge of the religion for the sake of this world and withholding that knowledge (i.e., not teaching people)
39. Betraying a trust
40. Recounting favors
41. Denying Allah's Decree
42. Listening to people's private conversations
43. Carrying gossip
44. Swearing
45. Breaking contracts
46. Believing in fortune-tellers
47. Behaving badly towards one’s husband
48. Making statues
49. Lamenting, wailing, tearing the clothing, and doing other things of this sort when an affliction falls
50. Treating others wrongfully
51. Treating one’s wife, servant, the weak, and animals badly
52. Offending one's neighbor
53. Offending and abusing Muslims
54. Offending people and having an arrogant attitude toward them
55. Trailing one's garment in pride
56. Wearing silk and gold (this is for men only)
57. Running away from one’s master (this is for slaves)
58. Slaughtering an animal that has been dedicated to anyone other than Allah
59. To knowingly ascribe one's paternity to a man other than one's biological father
60. Arguing and disputing violently
61. Withholding excess water
62. Giving short weight or measure
63. Feeling secure from Allah's Plan
64. Offending pious people
65. Not praying in congregation but praying alone without an excuse
66. Persistently missing Friday Prayer without any excuse
67. Usurping the rights of the heir through bequests (to others)
68. Deceiving and plotting evil
69. Spying for the enemy of the Muslims against Muslim's interest
70. Cursing or insulting any of the Companions of the Prophet

Source:The Major Sins(Al-Kaba’ir) by Muhammad ibn `Uthman Adh-Dhahabi

I'm sorry, but here you have mistaken. Shirk is not only a major sin, but the biggest sin, but the sins below shirk a major but are far better than shirk and are forgivable. What I mean is, even if the major sins which are below disbelief are not to be taken for granted even if they are forgivable, because a true believer does repent and tries not return to the sin.
So, abandoning prayer is somethimg forgivable, right? And not kufr? Is abandoning the prayer must be done with an intention in order to avoid kufr? Just in curiosity.