On the contrary, I think the theatrical cuts are the ones generally with pacing problems.
Fellowship of the Ring, for example, in its theatrical incarnation feels very uneven to me, with the Mines of Moria scene seeming like a climax due to the overall faster pace/momentum of the film. It is then horribly distracting when you realize there is an hour left to the film. The Extended Edition, though slower, feels far more deliberate and what was originally intended.
The Two Towers loses a lot of the emotional development, and I never particularly felt the Extended Cut to be particularly ponderous.
Return of the King is long in any incarnation, with both versions feeling like they have uneven pacing. I still prefer the Extended for the world building, but it’s a major mistake to show the Army of the Dead agree to Strider’s terms beforehand.