Same here. For example, Lamarck is very difficult for me to do, meanwhile Leconte is manageable. I think there are two specific reasons for this. First, the work has you below threshold for several portions which gives some relief to the muscles during the intervals themselves, and secondly, the rest between sets is longer, which gives more time to actively recover between them. Those steady threshold intervals are just relentless and the last couple minutes can feel like the final 30 seconds of a 3-min VO2 interval, so it takes some serious mental strength to push through in my experience.
In response to OP, a good way to gauge difficulty of the session is the IF. That often tells you what head space you’ll need to be in to complete the work. Anything above .90 IF generally is near or at race intensity, and it will feel intensely hard at points. Those longer steady state intervals you mention generally are an IF between .86 and .88, which feels considerably easier.