In the end, 40 days weren't enough to achieve what Damien wanted to achieve. The forces he was trying to control were out of reach for even Demigods, let alone mere lower existences like himself.
His improvements mainly took place mentally. He was comprehending the path forward so that he could walk it properly without making the same mistakes in the past.
But this was enough.
He didn't need to gain strength in a single month. He had at least another seven to continue improving himself to reach where he wanted to be.
And he was perfectly content with what he'd gained so far. Even if there wasn't a substantial increase in his current strength, his road forward would be much breezier because of the training he did now.
This type of forethought wasn't something he possessed before. Growing into his intelligence allowed him to make a decision that benefitted his future and allowed him to grow as a person.
What better result was there than this?