Well, personally I don't agree. All of the Dragon Ball series have their flaws, but I really liked what they were trying to pull with GT, and they succeeded in my opinion. Loved how the first half was goofy, full of adventure, exploration and discovery like in the original, and how the second half "switches gears" for a more DBZ-like experience.
I know that everyone has their opinions, but you are disregarding critical flaws here lol. Some characters were completely destroyed in GT such as Gohan and Trunks. Pan and Uub were missed opportunities and we barely saw others like Bra, but the writing has never been noteworthy in Dragonball. It was a big mess of older Dragonball material with kid Goku, transforming back into his adult body somehow in SSJ4 form. The lighthearted stuff was uninspired and the DBZ style battles sucked imo.
The biggest problem was that the creators of GT had absolutely no sense for the trademark battles. To use an analogy, I'd point toward wrestling and the art of ring psychology. That is to say, how to put together a match by using certain moves or doing something unexpected at specific moments in a match to engage the crowd.
You could tell that the creators of GT were clueless, as they looked at Dragonball Z and said: well, Goku has an iconic attack (Kamehameha) which look cool. Let's use this attack as many time as we can since the fans love it. As a result, the fights were completely brainless and I quickly got bored of seeing Goku relying mostly on his kamehameha attack over and over. -_-
This is something that Toriyama quickly understood while creating Dragonball, which is why Goku would use the attack once or twice during a fight. As the battle would go on, so would the anticipation to see him bust out his trademark techniques in one way or another (same for the spirit bomb). It's basic combat psychology which should be used in a shonen manga / anime based around drawn out battles, but sadly the creators of GT couldn't execute.