Lionel Messi marked his 500th appearance for the club with a goal and Luis Suarez scored twice after Heiko Westermann's first-half own goal on Wednesday.
The win saw Barca stay top of La Liga to finish a year which saw them win five trophies.
But Luis Enrique was unwilling to describe it as perfect as he urged his team to improve on their efforts.
"It's a very good year and I put nine because everything can be improved," he told reporters.
"I, as a player, based my philosophy on giving everything and never had anything to reproach myself, always finished every season well and as a coach I feel the same.
"We finish the year with overall satisfaction in all aspects."
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Barca were fortunate to go ahead just before the half-hour mark, with Neymar hitting a controversial penalty onto the crossbar, only for Westermann to put the rebound into his own goal.
Luis Enrique praised mid-table Betis for their effort, particularly in defence, having refused to criticise the referee for awarding the spot-kick.
"It has been very tight from the start," he added
"It is a credit to the intensity with which Betis has defended. We were not fluid."