Now this part is just corny af. Pretty sure MC reincarnated knowing he was both the strongest swordsman as well as mage in his previous lives. His confusion was implied to be more because he was trying to figure out why the people in the present (his past's future timeline) were weaker than people in the past, and why the Numbers have become essentially an evil syndicate. He knew he was OP so he declined being a high rank adventurer back when he first registered in the guild in previous chapters. He also knew he was OP so he never felt any urgency during his previous battles. Now they're attempting the whole "Seiken Tsukai no World Break" thing where "Oh, MC actually forgot 90% of all his abilities so he can get this *sspull now for some drama!"