The Brazilian went into last weekend's Singapore title decider with an outside shot at winning the title.
But DAMS driver Valsecchi sealed the crown in the first race of the weekend by finishing just ahead of his rival.
"I obviously feel a tang of disappointment, but I can't complain about my results across the season as a whole," said Razia.
"Lots of people wrote me off as a potential title contender, but I proved them wrong. I think I have improved hugely as a driver this season."
He also paid tribute to the efforts of his Arden team, which fought for the championship for the first time since Heikki Kovalainen lost out to Nico Rosberg in 2005.
"The team and I have shown we can compete at the very highest level," he said.
"Luck hasn't always been on out side, but we've fought back strongly in times of adversity and there isn't a great deal to choose between my results and Davide's.
"There has been a lot of hard work and nothing has been gifted to us, so we have to be satisfied."
Razia rounded out his season with a fifth and a fourth place finish, but he added that there was no reason to be disappointed with the final weekend of the campaign.
"It's a pity not to have finished with another podium, but we've had many of those this year, including four wins," he said.
"So I don't think we have any more to prove. This has been my best racing season to date. It has been a fantastic season and I'll always remember it fondly."