Tigers beat Wakefield 45-20 to end a 91-year wait for a top-flight title.
Powell's side secured top spot with four Super 8s games remaining and are the only team so far to confirm a place in the semi-finals.
"It is a journey, not a destination, this," Powell told BBC Radio Leeds.
"We are on the path towards being superb across a number of years.
"We have got right to the forefront of achieving our potential here as a group. And there is a long way to go."
Powell said the League Leaders' Shield, looked upon as the least important of the domestic honours, "should be prized", despite needing "to be polished up a little".
"This thing is awesome," he said.
"To be the most consistent team in the competition is special to me."
Powell has guided Tigers to Super League's summit in his fourth full season at Castleford, having taken over at the Jungle with the side bottom of table in May 2013.
His attention now turns to the northern hemisphere game's biggest occasion - Grand Final day at Old Trafford on 7 October.
"We will work hard towards winning the next four games and the Grand Final," Powell said.
Castleford boss Daryl Powell says clinching the League Leaders' Shield on Thursday marks the start of what he anticipates will be a "superb" few years for the Super League club.