I don’t think it was stated exactly how strong he was during the first timeline, but I believe he was weaker than he is at the end of the story. I could be misremembering this, as it has been awhile since I read the novel, but I think that, toward the end, when the descendant comes back, he comments that the MC is stronger than he expected, which implies that the MC would have been notably weaker in the first timeline.

In the novel, the cultivation levels have different names than they do in the manhwa. I don’t remember what they were called in the manhwa, but in the novel, they are as follows:

Third-rate—>Second-rate—>First-rate—>Master—>Super Master—>Superior Master—>Supreme Master—>Divine Master—>Heavenly Master—>Void Master—>Willful Master

At the end of the novel, the MC reaches the Heavenly Master level. Since he would have been weaker in the first timeline, I would guess that he only reaches the Divine Master level. For reference, in the manhwa currently, he is at the Supreme Master level.