The Baggies secured a 4-0 win over all-ready relegated Barnsley on the final day of the campaign with Karlan Grant netting a brace and Adam Reach and Matt Clarke also on target at The Hawthorns.
But while Albion ended the season with two wins and a draw, Bruce knows a mid-table finish wasn't good enough for a side with parachute payments and one of the largest wage budgets in the division.
Albion were in the play-offs when the former Newcastle boss replaced the sacked Valerien Ismael in February.
But he failed to win any of his first five games in charge - with that run effectively ending their promotion hopes.
"This season has not been good enough," said Bruce who has been tasked with overhauling Albion's squad for a promotion push next year.
"Looking back on the three months, it was the first month where I didn't make the impact I would have liked.
"We didn't get anywhere near the results that we needed to give us a chance.
"I couldn't address the slide quick enough and that is the overriding feeling I have at this moment in time.
"We finished okay. We've given a glimpse of how we want to try and approach it next year.
"But it was a little bit too late.
"We have got good players in the club and my challenge is to put a squad together that is capable of getting us to where we want to get to.
"We've got a big summer ahead."