Former Scotland and British and Irish Lions coach Telfer caused a stir with his comments in a national newspaper.
But wing Cuthbert, who scored the decisive try when Wales beat France to be crowned Six Nations Grand Slam champions last season, said: "It's his opinion, but I know how hard the boys work. We have shown in a lot of games where we come out on top as the fittest team, especially in last year's Six Nations, and hopefully we can show it again."
He added: "Everything we do (in preparation) is at a really high intensity to make sure we get as close as possible to that game standard. I've worked my a*** off since coming into professional rugby.
"From where I started, and being in this environment, my game has really progressed. I'm still developing and have a lot more to learn, but each game I will get more experienced."
Cuthbert's views were backed up by Wales' Six Nations attack coach Mark Jones, who added: "There is absolutely nothing lazy about the work ethic of the coaches or certainly the playing staff. Three Grand Slams in the last few years suggests being lazy isn't something that goes on here."
Cardiff Blues star Cuthbert will be an integral part of Wales' bid for a winning start to their Six Nations campaign when they tackle Ireland at the Millennium Stadium on Saturday.
Despite being just 13 caps into his Test career, the 22-year-old has carved a reputation as a prolific finisher and powerful runner with a prodigious work-rate and he will undoubtedly be on Warren Gatland's selection radar leading towards this summer's British and Irish Lions tour of Australia.
"I try to set myself a target of 15 or more touches in a game," Cuthbert said.
"Obviously, it's a high challenge to set, but we have got high expectations in the Wales camp and all the wingers and full-backs look to get as many touches as that. Rob Howley (Wales' interim head coach) gives us that licence to roam because we are big ball-carriers with good footwork. We look to exploit those gaps for mis-matches."