deck squats require more effort from me than regular squats from an endurance standpoint, I wonder why?

Is it a normal situation that deck squats require more effort compared to regular ass to grass squats? I mean you'd think that they should be easier or at least as difficult as a regular squat since the way I understand it deck squat is a momentum assisted regular squat?

Also if I can do the number of deck squats along with skiers required for mastery should I move on to the next element even if after completing the mastery standard for deck squats I feel very tired (I even feel a little lightheaded)? For some reason doing 5x15 of deck squats also feels like a cardio workout whereas doing 3x5 of a single leg squat doesn't  make me nearly as tired. Technique wise I never had any issues with deck squats and I learned how to do  them very quickly so doing a few reps every now and then doesn't present the slightest difficulty but doing multiple reps in a row is very exhausting for me.

I have no problem continuing working on deck squats until they become relatively effortless for the prescribed number of sets and reps but I also don't want to be missing out on the benefits of the later elements.

Yes -- it's more effort than deep squats.  You're actually putting your head on the ground, not just getting your bottom 6 inches off the ground.  The momentum isn't to really assist you standing up, just assist getting your balance out of the bottom position.

 

If you complete the reps with good form and good tempo, it's mastery.  You should feel tired -- it's a lot of work.  75 deck squats plus 50 skiers is a lot more reps than 30 (total) single leg squats.  Yes, it's cardio -- probably about 5:00 of constant full body full ROM motion.

thank you for your response, it's good to know that the movement is in fact difficult and that there's nothing wrong with me

But I still don't understand what I should  do, continue practicing deck squats until they become relatively effortless or should I move on to the next element immediately? 

Like I said before, if you complete the reps with good form and good tempo, it's mastery, so move on.  If your form/tempo isn't good, don't move on.  If you're not sure, post a video.

Something to also consider is whether you feel like you could reliably demonstrate Mastery again if called on to do so. If it was a "personal best" workout and you managed to gut through mastery, then I wouldn't consider that true mastery (but that's just my opinion so shouldn't be taken as the official word on the subject). If on the other hand it was an average workout and you feel that you could duplicate it consistently (even if you were tired at the end), then I would say it's mastery.