The 45L was just too big. If that wasn't obvious.
For the record I'm 5'7'' 165lbs dude. I'm also a competitive powerlifter.
I filled my 45L backpack with a large and small packing cube and took it as my main bag on a 4 day international trip. Lugging it through the airport it became clear that it was way too heavy. I found myself jealous of my girlfriend's roller. Especially when standing around waiting to board the plane, I was in agony. I took it off when we were standing in one place, but then because of how heavy it was, schooching forward in line got awkward when I had
to pick it up off the ground.
What's more, I didn't even use it fully expanded! Even the 35L mode with those packing cubes and everything else was too much. The bag itself weighs around 5lbs iirc, I think that combined with how dense and heavy the large packing cube full of clothes gets is what made the weight so unwieldy.
I wasn't a fan of the snaps either. Supposedly you can streamline the bag down from 35L but I found that if it was any more than 3/4ths full the snaps would just undo themselves.
I figure if 35L is too much capacity, the 45L backpack is a waste. I haven't taken the 30L on a trip yet, but I just packed for one and so far I'm liking it. My biggest concern was losing the front quick access zipper spot for my sunglasses, but the 30L's larger top access pocket has a smaller one inside that is perfect for my shades.
We'll see if I actually use it in the 33L capacity, but switching between 28L and 33L makes way more sense to me than switching between 35L and 45L.