That's one of the things that kinda bothered me about John in the DCAU. I totally get that when you're thinking on the fly you don't have time to imagine the most intricate and detailed construct, you go for whatever pops into your head first and its going to be basic but effective. That was John's usual approach in the show as he mostly just did generic energy blasts and bubble shields, but I feel there were times where they should've let him get more creative in the same vain as when he got turned into a kid and created a giant mech suit. I never really got "The Most Powerful Weapon in the Universe" vibe from the GL ring in the DCAU because of that.
In regards to the whole creating intricate things when generic constructs could do the job, I think it's a mental thing. Yeah they could just hurl giant detailess exploding blocks at people for big damage, but when say Hal throws a jet at someone, or John creates a tank, they have a better idea of the amount of damage they could/should do. Meaning that because of their familiarity with said objects, they have more faith in them and the damage they could/should do. The more they believe in it, the more gung ho they'll be about it and the more their willpower thrives. Just my hypothesis.
I do agree though, taking the time to put finger nails and knuckle hair on a fist construct and making jets/motorcycles to travel when they can just fly is stupid.