Hull went ahead for the second time through a try following what looked to be an obstruction and Tigers’ young debutant Calum Turner had a touchdown controversially disallowed in the second half, which would have got the visitors back into the contest.
“It is going back to needing video referees at every game,” said Powell.
“It is an absolute shambles, people running outside shoulder lines and nothing getting picked up. I cannot believe some of the lines being run today and not picked up.
“It was a shocking performance from the guy who refereed today, in the first half, in my opinion. Basic things that should be picked up were not picked up.
“I thought we started the game great, our defence was pretty tough, then we lost the ascendancy through, I thought, some terrible decisions.”
Injury-hit Tigers have dropped out of the leading quartet, but dug deep in the second half after trailing 20-6 at the break.
Powell insisted: “I thought we were great, I thought we were outstanding in the second half.
“I am pretty proud of our effort, it was more like us. They got away from us a bit at the end, but I think that scoreline is pretty harsh on us.
“I think we’ve got a massive amount to build on there.”
Hull had suffered a shock defeat at lowly Catalans Dragons in their previous game and coach Lee Radford was pleased with his players’ response.
He said: “To get off to that lead early was really important. I am pretty sure if we had started like that last week we’d have been in a lot stronger position to bring the result home.
“Castleford chased hard, but I thought we scrambled well when they posed some questions.”
Hull lost scrum-half Marc Sneyd soon after half-time with a medial collateral ligament (MCL) injury.
Papua New Guinea international Garry Lo been released by Castleford after making just one appearance for the club.
The 24-year-old has not featured since voluntarily assisting the police with an inquiry last month.
The club said in a statement: “Today we received a request from Garry Lo’s representative to be released from his contract with the club to allow him to focus on a personal matter.”
Lo joined from Sheffield Eagles last winter on a two-year deal but played just once in the recent loss at Wigan Warriors.