So since the Author confirm that Ancestor and Dou Di are only Sovereign Equivalent then the realm of BTTH and WDQK might be like this based on my understanding of that both Samsara and Half Saint are Pseudo Reincarnation and Dou Saint and both need to passed the Profound Life and Death to Samsara and Dou Venerate and Nine Turn Change to Half Saint before truly being a Reincarnation and Dou Saint.

{BTTH = WDQK}

1.) Dou Disciple = Tempered Body

2.) Dou Practitioner = Earthly Yuan

3.) Dou Master = Heavenly Yuan

4.) Dou GrandMaster = Yuan Dan

5.) Dou Spirit = Form Creation

6.) Dou King = Qi Creation

7.) Dou Emperor = Manifestation

8.) Dou Ancestor = Nirvana

9.) Dou Venerate = Profound Life

10.) Nine Turn Change = Profound Death

11.) Half Saint = Samsara

12.) Dou Saint = Reincarnation

13.) Dou God = Ancestor Stage

So with that ill give my understanding of who among the two MC's background are great and low.

Xiao Yan : we all know that the Xiao Clan was one of the 8 Ancient Clan that stand at the peak of Dou Qi Continent, but that was in the past thousands of years ago and the current Xiao Clan(currently name as Xiao Family) can't even be counted as a major force in an Empire and was barely hanging on in a certain city within an Empire with other two family battling for supremacy in that city with the current Xiao Clan/Family. And the current Xiao Family only had a Da Dou Shi as at best but that change only after the disaster of them being massacre and hunted by the Misty Cloud Sect with the Hall Of Souls being the true mastermind behind that attack, only after that they have produced more fighters of Dou GrandMaster and Up and that steadily getting up because of Xiao Yan's prestige around Dou Qi Continent rising up to the top and that prestige became a worship after becoming a Dou Di and fending off Hun Tian Di and the Hun Clan and Hall Of Souls and became know as the Flame Emperor that even resounded throughout the whole Great Thousand World all of the Xiao Clans current prestige came from Xiao Yan with him as the major support of the Xiao Clan and gained various connection and acquaintances.

Lin Dong : We know that he came from the branch of the Main Lin Clan that is one of the four great clan in the Great Yan Empire that has a powerhouse of Nirvana Stage and that is equivalent to a powerhouse of Dou Zong in BTTH. Even though Lin Dong only came from the branch family of the Lin Clan one cannot exclude that Lin Dong is still apart of it and the prestige of the Lin Clan rise because of Lin Dong being manage to enter the Dao Sect that helped his family and the Great Yan Empire rise to become one of the Supreme Tier Empire and that continuously rise with Lin Dong being the Second to achieve the Ancestor Stage after the Symbol Ancestor and fend off the Yimo Clan and became know as the Martial Ancestor that even resounded throughout the whole Great Thousand World.

Xiao Yan Being able to bring his clan from lowest that can't even be called a third rate clan to being the very top of the whole Dou Qi Continent.

Lin Dong being able to bring his clan from a second or third rate clan to the top of the TianXuan Continent.

So with this explanation of my understanding i say that Xiao Yan is the one with the lowest background compared to Lin Dong.

While the third MC we can rule him out of the three since he came from the 5 Great Ancient Clan that is known throughout the whole Great Thousand World and was only hidden due to him being a mix bloodline outside of his clan.

So if you have any other idea share it for me to understand.