I'm sure he made other suggestions, that he assumed were followed but were not, like the phasers being powered by the warp engines.
I'm not sure what this means. Are you saying that the idea for increasing phaser intensity by routing them through the warp drive was Kirk's idea? If so, why wouldn't he have thought about that while the Enterprise
was flying through the wormhole? Decker had to explain to him that the phasers wouldn't work in the event of engine imbalance.
No, the exact opposite actually.
In the novel by GR, once Decker explained why he countermanded Kirk's phaser order. Kirk was shocked since when he had seen that upgrade as an Admiral he had explained the many times a starship would need phasers when the warp drive might be down. And recommended they scrap the idea. He had assumed they would follow his recommendation.
He couldn't believe that the designers had ignored his opinion and installed it anyway.