The Villa skipper has been their standout player this season, scoring nine goals and creating eight more for a team fighting against relegation at the bottom of the table.
Grealish has been tipped to make a big-money move to Manchester United at the end of the campaign, regardless of whether Villa stay in the division or not, and Hourihane acknowledged that the 24-year-old has outgrown his boyhood club.
"He's top, top class. In terms of pure ability and sheer skill and technique level he's easily the best player I've played with to date," Hourihane told the Southern Star's podcast.
"He's just got that gift. He runs quicker with the ball, when he faces someone up you're in real trouble. He's skipping by the best players in this league so easily. He's developed over the three years I've been here – he's taken his game to a new level – especially this year in the Premier League.
"He's taken it by storm really. You know, England team and getting that big move is only a matter of time because, if I'm being brutally honest, he's too good for our team at Aston Villa."
Villa currently sit 19th in the Premier League table, two points from safety but with a game in hand.