The champion duo claimed every available major medal and trophy over the last year, including the Golden Boot and Dally M and Clive Churchill medals. On a team level, they secured a State of Origin series victory, a World Cup win, a Telstra Premiership and now a WCC triumph.
Bellamy said they don't always get the recognition they deserve.
"I was a really proud coach tonight," he said.
"To hold all those titles in the one year, but also individually for these two guys to hold the big individual awards – Dally M, Clive Churchill Medal and Golden boot, they hold between them. That's quite remarkable.
''Sometimes I think they don't get the accolades they deserve because they are probably in Melbourne and not so much in NRL heartland.
"But I know how good they are and how highly this club holds these two players. To do what they did tonight and hold all those records is quite unbelievable, especially they are grandpas now as far as NRL goes."
Slater injured his shoulder reaching out from the in-goal area in the first half, but the coach is hopeful it isn't major.
"He's OK, I think. We think it is a jarring of the shoulder, but again it was more a precaution than anything else. The doctor thought that was the best way to go. I just think there's not too much alarms bells in the dressing room at the moment, so hopefully that is the case."
Bellamy was pleased at his side's performance they'd only been training as a full group for the past few weeks.
"Our completions were really good," he said.
"They fell away a little bit in the second half, but we did a really great job defensively.
"Sometimes it is hard to get a gauge on where you are at, at this time of the season. But I really liked what I saw."
The Storm curbed the Super League champions' all-out attacking approach and had strong performances from man-of-the-match Nelson Asofa-Solomona, halfback Brodie Croft and lock Dale Finucane.
"From what I saw of Leeds, they don't go away, and we hung in defensively," Bellamy said.
"We blew a bit of steam out of them, and they struggled in the second half with the footy.
"I thought it was a really good performance."