I actually think some of DT's best music of all time comes from their 10-15 minute songs, give or take. In DT12 there wasn't any of that, and I feel like some of the songs could have been longer without sacrificing any attention or entertainment value.
Just as an example, I feel like The Looking Glass and Behind The Veil felt a bit rushed. I know the idea for DT12 was to make brief, shorter songs, and they definitely succeeded (I'm actually surprised at how well they were able to make these shorter songs feel grandiose on their own), but I also think their best musical abilities come when they elaborate on musical ideas. Not with songs like, say, ANTR or TMOLS, though I'm actually an avid lover of both of those. Songs like those are good when it isn't JUST longer ones like that (looking at you, Black Clouds).
I apologize for the somewhat meaningless rambling though
Basically, long songs are good, just not too long/too many
In my opinion.
I loved the longer songs on ADTOE though, they all felt very well balanced. The only problem with ADTOE is that it was pretty safe, but the songwriting could be filed under some of DT's best (yes, some of the songwriting on ADTOE is very similar to or taken directly from Images, but I just mean certain individual things. The instrumental section in Outcry, for example, is pure genius in my opinion.)