I've got to disagree with this. Aldo continues to grow and improve technically. It's likely true that he doesn't possess the same explosive athleticism that he did in his younger years, but that doesn't make him worse. He's less dangerous, you might say, but definitely better all around.
For one, his boxing has improved by leaps and bounds. He now has arguably the best jab in MMA, and his combination punching is better than ever before. So, too, is his footwork, and the way in which he uses it. He can pivot and side-step like few others in MMA, and his cagecraft is great. He used to back himself into the cage all the time, but that happens less and less with each fight. He's also an excellent counter puncher, both going forward and retreating, and that makes him dangerous no matter where the fight goes.
Honestly, I think the majority of his fights being "close" has to do with his nature as a fighter. He loves beating people in their element, and opponents are so afraid of attacking him that he never feels pressured to push the pace. When Mendes brought the war to him, we saw a level that Aldo hasn't shown in years, because he hasn't had to. This is a sort of weakness in itself, but the fact that Aldo is a tactician doesn't mean that he's regressing.