There are multiple things at play here imo
Firstly, yeah, the budget definitely feels like it has taken a hit, primarily on the animation itself.
Secondly, as a board artist, I'm just noticing a lot of really flat or stiff staging choices. The first couple seasons definitely had more of this than I originally remembered, same with the fluctuation between animation quality. Not every episode looked as nice as that opening two-parter...
But thirdly, the character designs are altered in a way that's probably hurting line mileage. Phil Bourassa has been DC's go-to artist for god-knows how long at this point. He was design lead on Young Justice, and the majority of their DTV output. But the first couple seasons were a
lot more streamlined. This season has a lot more in common with the DTV style, with a lot more complex shapes, anatomy, lighting, and detailing. Look at the difference between Batman in this season and previous seasons.
Even those seemingly minor changes to the demands of anatomy and lighting really add up when you're drawing extra cheekbone details, or extra lines to shape everyone's torsos.