Well... yes... but mostly no. What you're describing is trying to fill in the gaps between something like for example the Arlong Park story and the siege of Marineford. LOTS of plot happened... sooo much plot. you don't really need to know all of it though. seeing Crocodile as Luffy's ally is probably the biggest shock TBH.
well, part of that is that Toriyama-sama kinda wanted to quit writing DB and his publishers would periodically tell him how much money he'd get if he did a new story arc. So Toriyama stares at the ¥¥¥¥¥¥¥¥ and writes some more Dragon Ball then goes back to what his true passion is... writing comedy mangas(and games like Dragon Quest). Yeah, this is why DBZ has so many prat fall moments.
Enh, most of DB isn't relevant later..... especially Yamcha. :Þ
Welp, prior to Toyotara-san's involvement the main secondary writer was Takao Koyama. He wrote most of the DBZ movies and his student Aya Matsui was head writer on GT. Thing is... Toriyama-sama still did some character design work for those... he just didn't write the story. Koyama-san is a talented writer, but he's more of a screenwriter than a manga-ka. The mangas he's been involved with were drawn by someone else, sometimes Katsuyoshi Nakatsuru, who's also worked on a lot of Dragon Ball stuff(and most notable perhaps is he's the guy who came up with the appearance of the SS4 form).
Koyama-san is the guy who wrote the second Broly movie, and that had one of the best Videl appearances I think. Like Koyama-san actually has scenes where Videl fights BROLY! It's not played for laughs though. That's one thing that's a noticeable difference between Koyama-san's work and Toriyama-sama. Koyama-san's not as big on prat falls. He puts in bits of humor, but it's a different kind of humor. i guess you could compare it to sitcoms.
But yeah it's very true that at this point the majority of the actual writing for Dragon Ball is not actually Toriyama's.