So... if you really need to drop a 2/1 first striker at instant speed, you could cast this, targeting a creature you control, sacrifice that creature, attempt to counter the spell for lack of valid targets, transform it, resolve it and block. Which is all kinds of cool, but I wonder how many people would think of that...

I ran into similar problems with "If ~ would be countered" - too many things counter a spell that you really don't think will. Unless you want "Oh, I didn't tap any mana, oops" to be a legal way of faking it into play, you need something like "If ~ would be countered by a spell or ability" which is yucky.

V is of course exaggerating. Spells can be countered by spells (Cancel), abilities (Voidmage Prodigy, Voidmage Apprentice), or the rules of the game. The rules will counter a spell at just one point - the moment it would begin to resolve - and under just one circumstance: if all its targets are illegal (no longer there, no longer fit the targeting description, or have become illegal for other reasons such as shroud or protection).

I assumed this cycle was deliberately made fairly easy to counter by the rules of the game, by making them all target just one creature. I assumed that was the reason for this cycle to exist, as otherwise they're a cycle of spells with a weird blue-hosing clause.

It was. Every set needs some utility spells, but doesn't it suck when your opponents sacs the target and gets some last benefit? This way it's a win-win, which means your opponent loses.