The former defender says his side fully deserved their fourth-successive Eredivisie crown having beaten nearest rivals Feyenoord, Twente and PSV in 2014
The Amsterdam outfit were crowned champions after a 1-1 draw at Heracles, with Lasse Schone opening the scoring for Ajax in the 13th minute before Simon Cziommer equalised nine minutes later.
Sunday's celebrations were a far cry from the previous weekend, when Ajax were thumped 5-1 by Zwolle in the final of the KNVB Beker.
However, De Boer - who won five titles with Ajax as a player - took delight from his fourth crown as a coach, pointing to results against their direct title rivals as a key factor.
"We've beaten almost all our direct competitors. The title is justified," he said.
"I am proud. It was not the prettiest game, but eventually we dragged in the title.
"If we see that after the winter break we beat Feyenoord, Twente and PSV and drew with Vitesse, then we are worthy champions.
"Over the whole season we've been the best."