The Wales international moved from Celtic Park earlier this summer.
Wales coach Roberts praised Matthews' decision to move back to England after a four year spell in Glasgow, with his country looking odds on to qualify for the European Championships in France next year.
"Playing regularly in the Premier League increases competition within our squad," Roberts told BBC Sport.
"And that's what we require."
The Welshman was quick to emphasise that though the Scottish champions were a big club themselves, the chance for Matthews to test himself against the international stars in the Premier League was something that could only be of benefit to the Dragons.
"Adam's done well up at Celtic," Roberts added.
"Obviously it's a big club, great history, [with a] great tradition, but it's the right time for him now to come back into the Premier League.
"It's a good challenge for him at Sunderland; a big club and there'll be good competition for places, which he'll need.
"And also there's that opportunity then to be playing against top players… on a regular basis.
"That will only help his development in the next step of his career."
Once one of Wales' most promising youngsters, Matthews has won plenty of silverware at Celtic, including four successive league trophies. But he hasn't featured for his country since 2013, and will be hoping that games in the English top flight would ensure he challenges Chris Gunter and Jazz Richards for a starting role, two players who play their football in the Championship.