Yep, that is the reason. Sometimes I don't wanna swing and that happes far more often than the 1 toughness matters.
I've been testing a prowess version similar to LoC's with
Thing in the Ice,
Scourge Wolf,
Alchemist's Vial and
Evolving Wilds instead of taplands to trigger delirium reliably.
Good things first: For some reason I didn't have mana issues with 5 Islands, 8 Mountains, 2 Sulfur, 2 Furmarole and 4 Wilds. Even the untapped double red on turn 2 was usually no problem.
Unfortunately everything else felt much slower than usual. In order to get delirium, I always had to sac a Wilds and a Vial. However, this is way too slow for what the deck wants to do. Vial eats 3 mana and does basically nothing, if you just wanna get it into the yard and don't wait until it can disable something important. This might not sound like much, but wasting 3 mana in an aggro deck is huge.
Of course you don't have to rush it, but without delirium I always wished my
Scourge Wolf was any prowess creature for a few extra damage here and there. This adds up to the point where a single buffed delirium Wolf attack won't even make up for it anymore. Also, the longer this Vial sits in your hand, the more you wish it was something else instead.
Next problem: He eats removal like a boss. Don't confuse this with the old "dies to removal" argument. What I mean is that if all the effort is worthless 90% of the time, I see no reason to cripple the rest of my deck for this guy.
Expedite doesn't help much either, because that's already 3 red mana, add another one or two for the buff and possibly some to get him through. Yes, when the stars align it's possible, but usually not. This means he sits on the board for a turn, asking to get shot.
Let's move on to my experience with
Thing in the Ice: The first thing I noticed is that I like it even less in the
Scourge Wolf version, because
Alchemist's Vial doesn't trigger it and once again, I always wished the Vial was something else. After I was certain that
Scourge Wolf isn't worth the effort, I went back to Entanglers and added
Thing in the Ice in there. Played for multiple hours straight and it transformed 3 times. It was never required for the win.
This card gives me headaches. When I play it early, so that it profits from future spells, it just sits there for a few turns and finally gets removed before it's too late. That's still a 1 for 1 trade (unless it was a sweeper), but any other creature would've dealt some damage in the meantime. However, when I save it for later, I often don't have enough instants left to flip it immediately, either. The worst case scenario is when I sit on
Expedite in topdeck mode and could swing for the win, but draw a wall...
It looks incredible on paper and you'd expect it to be right at home in a deck full of cheap spells, but it's not an aggressive card and not even a Prowess deck is able to turn it into one. It's a card for spellheavy decks that want to stall into lategame - a defender that needs to be dealt with. What this deck needs is an attacker that needs to be dealt with.