TBH I always found him to be quite overrated. Sure, he looked good against James Thompson and Ricardo Morais, but he got his shit pushed in by Cro Cop, was nearly KO'd by Kharitonov who only lost because he had no fight IQ and tried to shoot on Aleks, and couldn't even put away Josh Barnett in a straight-up kickboxing match during which time Barnett handled himself well and helped Aleks along as he gassed by working him over with great body shots. It's true enough to say that with more discipline he could've been better than he was, but to act like he was six months of hard training away from being able to run roughshod over the HW division is quite a stretch.
Just in that 2006 OWGP, he was beaten by Barnett, he would've for sure been beaten by Cro Cop and Nogueira, he would've likely been beaten by Werdum, Overeem, and Hunt, and he may have even been beaten by Wanderlei and Fujita. As for the UFC fighters of that era, in no universe would he have been able to deal with Tim Sylvia's reach and boxing, unless he clipped the chinny Arlovski (always a possibility) he would've gotten brutalized by him, Couture would've gassed him in the clinch and taken him down and beat him up, Jeff Monson would've been able to north/south choke him in 2006-2008 just as he did in 2013, even Gonzaga could've probably fucked him up on the feet with his power and he definitely would've had the advantage on the ground.
In short, Aleks was a solid fighter who had the potential for more but was never truly elite and probably even at his best would've been lucky to be in the bottom of the HW top 10.