The West Yorkshire club, playing just five days after their Challenge Cup semi-final win, saw one of their eight interchanges taken away after making a late change to their 21-man squad.
Castleford said they saw three players unable to get through their final training session on Wednesday and - because of that - they drafted 17-year-old Academy winger Jason Qareqare in for a shock debut.
The youngster excelled, remarkably scoring a brilliant try after just 45 seconds and with his first touch, but the under-strength hosts eventually went down 30-12.
RFL rules say that if changes are made to the 21-man squad, clubs will lose an interchange.
But Powell - whose side have now lost four successive Super League games ahead of Wednesday’s derby at Wakefield Trinity - was irate given the circumstances.
“We lost three players in the team run and we just decided (on Qareqare),” he explained.
“It was an unbelievable first touch for Qareqare.
“I was really pleased about that and I made up for him. I thought he was great today.
“For a young bloke to make his debut and then do that with his first touch was fantastic.
“Out of all today, there wasn’t a lot to cheer about with our game and the game as a whole was a really low quality affair. But that was worth getting on your feet.
“He’s still at school and he trains with us in school holidays and at weekends at times and he’s just always been accomplished in what he’s done.
“He’s a mature young fella. But he didn’t train with us. It is funny… he didn’t even do the team run!
“And the RFL reduced us a sub today because we brought him in from outside the 21 which I think is a sham. It’s absolutely terrible.
“I don’t get 21-man squads anyway but to take a sub off us today was appalling.”
Both sides were playing in the televised game having featured in semi-finals on Saturday, Hull missing out on Wembley after losing to St Helens.
Powell, who was missing six players who featured against Warrington, was not surprised it was a low quality contest.
“Slow and painful,” he said, when asked to sum it up.
“ It was hard for both teams. I’d like to question the understanding of five-day turnarounds which both teams have had to do there and what a player has to go through on a five-day turnaround I think is too difficult.
“You’ve seen with our team today we had to push quite a few players for the semi-final and that put us under pressure today.
“We battled hard but either side of half-time did for us really and we couldn’t quite get the game back.
“It was tough for us today. Really tough. We couldn't get our game together.
“We lost both our pivots and full-back from the semi which then moved our nine to half-back . Most teams would struggle with that.
“We hung in there but yesterday morning three players pulled out of our team run which is a regular occurrence at the moment.
“Obviously, the boys are creaking. They are just creaking.
“You can’t train with a five day turnaround. Anyone who’s played rugby league, you know how sore you are, especially one a five day turnaround.
“You just don't train. You do one session - a team run. We’re pushing players until the last day to give them a chance and they just couldn’t do it. It’s been tough. Wait until you get to August… good luck with that!
“We want the games to be high quality. Both teams played in a semi-final and that game wasn’t where you’d want it to be tonight.”