Kennelly played 158 games of AFL football but called time on his career on Thursday, saying the rigours of elite level Australian football were taking their toll on his body.
Roos said Kennelly has scaled the ultimate heights in his adopted game and would fare well under any comparison.
"I think Jim and Tadhg are the two that stand out. Obviously Jim won a Brownlow Medal, which is something that's held in high regard while Tadhg's won a premiership," Roos said.
"And those two things are very significant, so I think you've got to say the two most successful Irish players have been Stynes and Kennelly.
Stynes forged a path for players like Kennelly when he arrived in Australia to play AFL with Melbourne in the 1980s. He played 264 games for the Dees until 1998 and won the Brownlow in 1991.
Roos added that he'd enjoyed watching Kennelly's development since he arrived as a raw recruit from Gaelic Football, but came to realise that injuries were beginning to limit the rebounding defender.
A knee injury restricted his 2007 season to just 13 games, with dislocated shoulders and hernias further restricting his contribution.
"I've seen him develop into a great player but seeing him over the last two years I can sense he's been frustrated [by the injuries]," said Roos.
Kennelly, 27, is due to fly back to Ireland in the next few days to restart a career in the Gaelic Football competition.
"The decision today has come as a shock to pretty much everyone at the club. But if he didn’t' go back now he wouldn't be able to fulfil the ambition that he did have," said Roos.
"And he's extremely concerned about the last two years and the injuries that he's had and the ability to make an impact at AFL level, and make an impact in the new career he'll take over.
"I'm absolutely convinced he's making the right decision. The easiest decision would've been to continue on at the footy club and go through the motions.
Kennelly, a member of the Swans' 2005 premiership winning side, said today's decision to head home was a combination of injury concerns and his wish to spend more time with this family.
