He's more efficient than Thomas.
Not really. Thomas posted a .625 TS% scoring efficiency that season. Irving has been fantastic, but at .602 TS trails Thomas' scoring efficiency.
The reason is that Thomas excelled at getting to the FT line. Thomas got to the FT line a whopping 5 more times every 36 minutes. And this is a huge difference. Not only because of scoring efficiency, but because it creates foul pressure on the other team, getting their players in foul trouble and affecting the other coache's rotations.
And while Kyrie has a slightly better AST/TO ratio, overall, Thomas turned the ball over at a minuscule 10.4% TOV% rate, which is quite a bit lower than Kyrie's still excellent 12.1% TOV% rate.
In terms of overall productivity, Thomas accrued Win Shares at a whopping .234 WS/48 rate (7th in the NBA that season) that season, ending up at a whopping 12.5 Win Shares (9th). In historical terms, that season by Thomas ranked as the 9th highest WS by a Boston player in the 3-PT era, and 6th highest WS/48 rate. Only Larry Bird, McHale, KG & Pierce ever posted higher total WS in a season and only Bird & KG ever posted a higher WS/48 rate in the 3PT era. Even when you expand it to all of Celtic history, the only names that sneak in above him are names like Russell, Macauley & Sam Jones. In terms of total points & assists, that season by IT is in the rare company of Bird & Havlicek for 2000 points & 400 assists. His prior (2015-16) season was also in their exclusive company in the 1800/500 club.
Irving, again, has been fantastic, but trails in this efficiency at .204 WS/48 (ranked 9th this season) and, assuming he plays all remaining games of this season, is on pace for a total of 10.4 WS (he's currently ranked 15th). If Kyrie stays healthy and plays in all remaining games, he should be able to join IT, Bird & Havlicek in the 1800/500 club.
All that said, Irving has, indeed been excellent this season in terms of offensive efficiency and production. That he is trailing that particular season by Thomas should in no way be considered a negative. His numbers are without any doubt as good as we could reasonably hope for from him, considering that his productivity numbers this year are at or near career highs and all are easily more than All-Star level. They just aren't quite up there with what Thomas achieved in that special season before his hip failed him.
By all accounts, he's a better mentor to the young players than Thomas was and has more leadership qualities.
I don't really know how you can be sure of this. This is just speculation.
The team that currently surrounds Irving is very different than the one that surrounded Thomas. Far, far more talented.