I wouldn't say he's absolutely awful nor would I say he figured it out at age 30. I would say the defense was designed with Lopez in mind.
Lopez is one of the slowest players laterally in the league. He had a 12.77 sec lane agility at the 2008 combine. For context, Harry Giles had a 11.08 sec, Barnes was 10.93 sec. Cs coming out this year like Claxton (11.26 sec), Fernando (11.29 sec), Gafford (11.61 sec), Hayes (11.74 sec), & Kabengele (11.21 sec) are much quicker. Plain & simple, Lopez doesn't really have a shot at defending players on the perimeter.
The Bucks accepted that fact and opted for a deep drop on pick & rolls. That is susceptible to good pull-up players (especially good pull-up players from three), but it helped improve the overall effectiveness of their defense and allowed for nothing easy at the rim. The Kings would need to employ a similar concept while relying on Fox & Ferrell to go over the screens and force their man into the midrange area. Now the opposing player has a man behind him (no 3pt shot), and a 260lbs C w/ a massive 9'5" standing reach & 7'5.5" wingspan in front of him to challenge a close shot. We'd have to live with the midrange shot which analytics tell us is a great thing to live with.
When he's off the floor and you have a Giles/Bagley combo, you can probably employ a switching or hedging strategy on the pick & roll considering their athleticism/quickness and lack of elite shot blocking abilities at the rim.
Here's an interesting read on Lopez's defense with the Bucks:
https://www.brewhoop.com/2019/1/17/...nse-built-around-brook-lopez-mike-budenholzer