After a disappointing European Cup semi-final exit to Toulon, Penney's side responded with a resounding 55-12 win over Edinburgh.
It was a match in which Penney made 11 changes and he believes the strength in depth at his disposal shows how far his team have come.
"It's been a long season and the growth of the group has been terrific," said Penney.
"On the back of a six day turn around and the disappointment of Marseille, to have to fly back out to an Edinburgh side who have been difficult was a tough one - to put 50 points on them was really pleasing and I'm very proud of the group.
"Up until the past 12 months the word 'transition' was being used an awful lot about this team.
"One of the most pleasing things is that it hasn't been used in the last 12 months.
"When you lose somebody of Doug Howlett and Ronan O'Gara's ilk in one hit, let alone all the other boys, it's not easy.
"However there's been no mention of or calls to bring those guys back because of the great job the young guys have done in stepping into their mammoth void."
Follow us on Facebook, join the conversation on Twitter, sign up to our YouTube channel for extensive match highlights and sign up for our newsletter for regular updates on the RaboDirect PRO12