The Blues beat Manchester City to the signing Cucurella, who impressed many while at Brighton, in a deal which raised eyebrows due to its size.
The 24-year-old has struggled, along with a number of his team-mates, during the early days of his Chelsea career, and saw left-back rival Ben Chilwell score one and assist another in a brief matchwinning cameo against West Ham on Saturday.
Agbonlahor has described the former Barcelona youngster as "not good technically" and "very erratic", and suggested the money spent would have been better served on Rice.
"I don't like watching them play football," Agbonlahor said on talkSPORT. "It's boring. The first half - boring, boring Chelsea. Chelsea fans agreed midweek. Watching them at the moment is boring football.
"The five at the back, when you watch them, it's not working. they put Chilwell on for [Marc] Cucurella. Chilwell's flying forward, scores a goal.
[Cucurella], I'm not having him. I don't understand [spending] £60m. He's not good technically, very erratic. Silly fouls.
"Put that towards Declan Rice. I thought Chelsea got away with one and West Ham were very unlucky not to get a point."