Yeah, I disagree. I'm not suggesting that I design encounters blindly. Of course I layer in effects designed to prevent thinks like the proverbial 1 BBEG easy topple encounter.
And when I play with a skilled, power-gamey group, I tweak the CR level upward and add in additional challenges (more three dimensional conflict spaces, etc.)
But once I think about the rules and fold in things that have an internal logic and consistency, I get absolutely no fun from blonking an encounter with big cheats on my side.
I also like being surprised by my players. Unlike some DMs, I require rule-loyal PCs, but I don't do pre-audits.
But I don't think even with your philosophical approach, this spell. works. Your assessment of it just strikes me as weird.
Consider this factual description.
1. It's a never-ending ammo clip. 2. It's apparently a silent supernatural ability and can be thrown without cluing enemies that the PC is in fact a spellcaster. 3. It's not subject to counterspells. 4. It doesn't trigger an AOO. 5. It's not limited by Hit Dice, unlike its Sleep counterpart. 6. It's a SOD spell that will always scale relatively high on its Will save. 7. There is a significant list of VERY powerful monsters, high CR, that are highly vulnerable to this spell. 8. The 30' foot automatic hit range increment is actually very generous, compared to comparably powerful spells that require either a touch or ranged touch attack.
That's a pretty long list of boffo attributes for one magical effect which CAN BE GAINED AT FIRST LEVEL.
Bottom line? That's just not the same as buffing a barb or using a clever area of effect spell.