Dragons’ matchday squad in Montpellier featured 13 players who came through their academy.
Lock Ben Carter, blind-side flanker Ryan Woodman, hooker Brodie Coghlan and currently injured scrum-half Che Hope have made big improvements this season.
“All the players will be better for the experience of Montpellier and what has gone on over the last 12 months,” said Rees.
“You review and help them grow individually, while ultimately you have to back those players up with a little bit of quality that comes in.
“Yes, they are losing Wainwright but they have also recruited and there will be a couple more coming in.
“You slowly build that strength in depth, and that is how a team and individuals grow.”
The hope will be that full-back Huw Anderson, who was lively off the bench in the semi-final, back-row forwards Harry Beddall and Evan Minto and loose-head Jordan Morris can follow the lead of those who have flourished this year.
Dragons have used 49 players this season but the Challenge Cup group stage hammering at Benetton, when the Italians scored 11 tries in a 74-21 victory, exposed their lack of depth in certain areas.
Cardiff were able to rotate while combining a URC play-off challenge with qualifying for the European knockout stages.
Dragons, who enjoyed a budget increase after signing a new Professional Rugby Agreement last year, are not quite there yet as they play catch-up with Welsh rivals after seasons of being underfunded.