Tigers finished 10 points clear of second-placed Leeds on the table and beat Rhinos four times during the year, including a 66-10 drubbing in March.
But they fell well below their high standards on the big stage and only Alex Foster’s try - converted by Luke Gale - on the last play of the game prevented them becoming the first team to be nilled in a Grand Final.
It was a heartbreaking end to a season which saw Tigers top the table for the first time in their history.
“It was tough conditions, but we couldn’t quite get a grip of what we were doing with the ball,” Powell said.
“We made a lot of errors, just basic stuff. It is hugely disappointing.
“We made 18 errors, 10 in the second half. I didn’t think we could get any worse with ball retention, but we managed to achieve that in the second.
“We couldn’t sustain or build any pressure on Leeds at all.
“We did that to ourselves really. I am disappointed we didn’t do ourselves justice.
“Leeds didn’t see the best of us and they were pretty good I thought.
“They massively deserved the win. We were nowhere near and that’s the most disappointing thing.”
Tigers were without Dream Team full-back Zak Hardaker who was dropped for breaching club rules.
Asked if Hardaker has a future at the club, Powell said: “I can’t really comment.
“I think it will come out in due course. It is nothing to do with me, that, but you will all be aware of that pretty quickly I think.”