Jefferson isn't the move everyone was hoping for (i.e., the young wing with some upside), but he's a decent addition to the team as the 9th or 10th man in the rotation IF he plays the way he did in Dallas and not Utah.
I think what Griffin is thinking here is that James playing the first 7 minutes of the first and then coming back to play 10+ minutes in the second quarter with the defensive lineups and then with Love and Kyrie back in and then repeating in the second half or playing all the of the third quarter to push for a blowout can get us big enough leads to rest him in the fourth. Jefferson, Mo, and if healthy (sigh), AV can play bench minutes that Miller, Jones, Harris, et. al. played and blew big leads prompting James to stay in longer games or to re-enter games that looked over. If so, James can play 32-34 minutes per game. We'll see.
Griffin is looking for a a player that can truly make an impact in the top 8 of the rotation and for that to happen, that player has to be a plus player and a player such as that is hard to find for a vet min unless David West falls into your lap. A TPE might help us find that player next year and I hope we keep looking because stacking the deck even more in our favor should be a priority no matter how good this team looks.
I think Griffin means it when he says a team that went 33-3 with an SRS (10 teams or so in NBA history can boast this--will post more about it some time later) of nearly 13 is a team you want to maintain. Statistically, that stretch of games was better than any of what James's Heat teams did and better than the Heat's 27 game win streak if you look at opponent strength, MOV, SRS, etc. We may think that a player may improve us, but a team that's 33-3 and invincible at home takes the exact right type of players to improve. It's far more likely the pieces we have with the addition of team chemistry will perform better than a group with a new addition to the top 8 who's barely a plus player.
I know I have posted the below chart before (the numbers changed slightly with the last update of RPM), but we have nearly 8 of 8 plus players at the top of the rotation, with Delly being a plus player the final 30 games of the season, and 5 of those guys are young enough to improve. NO team has had the top 8 in its rotation be plus players although some have had 9th or 10th men be plus players. Not the Spurs these two years nor the Warriors. The Warriors improved by adding nobody, but with Curry (was a plus defender for the first time in his career) and Draymond taking big leaps as well as Barnes rising defensively. IF Kyrie is even a neutral defender, there's a really good change that this team while healthy can win 67+ games. Remember, the GSW's starting lineup had a DRTG of 97 and Cleveland's Kyrie/JR/LBJ/Love/Moz starting lineup had a DRTG of 98 WITH Kyrie being a negative defender and JR being poor in many aspects of defense and Love truly improving defensively for the first or second time in his career. If Shump starts and Kyrie improves defensively and we communicate the way we did at the end of the season, that DRTG can be lowered further. How good this team will ultimately be will not be decided by a 10th or 11th man, but finding players who can play in certain matchups is definitely advantageous. How good this team can ultimately be will depend on how much of a leap TT, Love, and Kyrie make and whether or not James is more efficient next year as this was his 2nd or 3rd least efficient year based on ORTG and WS48 and if lady luck sees us healthy. Griffin knows this and will not change things unless a "sure fire" opportunity arises but there are VERY FEW sure things who will improve 33-3.