Okay. I was wrong on Sankt altar, my fault. Though I would appreciate a scan of such.
The First spinjitsu master also has precognition, so it's far more likely that the two forms of precognition would cause them to cancel each other out, not to mention that The First also can rewind time.
However, essentially, The First has far more ways to defeat Yhwach than vice versa. He has a plethora of elemental powers that could beat him down. Has more versatily weaponry. He can BFR Yhwach, defeat him with mind manipulation, limit his mobility with gravity manipulation and telekinesis, can potentially copy Yhwach's own ability and use it against him, and weaken his through poison.
There may be others, but Yhwach's only shot at beating him, is essentially managing to strike a critical blow through the almighty. But that's difficult when The First can not only slow down time, but accelerate it, rewind it (which directly counters the Almighty's rewriting of the future as he can simply rewind it to before it was rewritten) and straight up stop it.
The First simply has far more ways to win, on top of being unaffected by Yhwach's Almighty, due to his acasuality with the golden weapons, he can also counter it with his own time manipulation. But with Yhwach's strongest asset gone, he falls victim to The First's other hax. He's not going to get close enough to the first to use his power nullification before The First hits him with some of his hax.