For the most part MFB or Burst don't handle returning characters that well, but MFB is a lot better at it in my opinion. There's some, if somewhat superfluous examples such as Tetsuya no longer showing his trait to cheat in Metal Masters, or how we eventually see how bladers such as Aguma and Bao are on good terms with their former enemies, the Beylin Temple with Zero G's cameo. There are bigger examples like Tsubasa and Yu getting more to do in Metal Masters, and even a little bit during Fury, despite not having a new toy to sell or being as major as some other characters (until Zero G forgot about Yu), Tsubasa has a story that followed the previous season's. For better or worse, we have the Garcia's, seemingly just minor antagonists, but actually become major in Zero G, with consistent motivations calling back to Argo's rivalry with Tsubasa.
On the flip side, we don't see many of the Dark Nebula bladers at all, Dan and Reiki are only cameos at best, not even a name mention. Team Excalibur was especially horrendous since Metal Fury only had them in one episode and didn't do much, but at least we can see that Julius is okay, and clearly more humble. Kyoya and Kenta not being in Zero G save for a cameo? Come on now. Characters like Benkei are heavily underused and shafted but his character's existence isn't a total waste either. MFB is far from great but we can often appreciate what they try to do for returning characters that aren't just the big major ones.
Now for Burst, they are terrible at using most of their characters. I can easily list the many, many, MANY characters who basically get Thanos snapped whenever a new season rolls around the corner, as if to say "Okay you have nothing more to sell, now go away", but you know this already. Oh sure, they'll remember Free, Shu, Valt, Lui, but let's really think about this. Free got nothing much to do after God, but you could arguably appreciate how much kinder he becomes... but the problem is that he appears time and time again without anything interesting, it becomes very stale. Lean seemed to have something for Free by defeating him, but they botched it up so badly that Free is the ONLY Sparking blader in the tournament to never ever fight Lean directly! How is that even possible?! What a waste. The legends mostly serve as just goal posts for the new main character of the week to surpass. Rantaro is semi-reoccurring, too bad that the show can easily replace him with another Kiyama brother and Valt seemingly never brings him up when his replacement is around.
Speaking of Valt, he has quite the nasty habit of forgetting his friends until they happened to be there. Even when they go back to the Beyclub setting in DB, Valt never ever brings up Kensuke, Daina or Cuza, not even Xhaka! He completely forgets about his new favourite bladers of the week such as Aiga, Drum or the Asahi bros in DB. Valt only remembers Rantaro in Sparking, but as soon as he's gone, nope he has goldfish memory.
The only cameos we do get is Amane, which is just a blink and you'll miss it cameo in Sparking. I do like that Aiga actually remembers his friends like Ranjiro, Souh and Fubuki in GT, that was cool of him. Isn't that right Valt? Sisco, Rantaro and Ranjiro did return in Sparking yes, but they only came back for marketing purposes, when they happened to have a new toy to sell. Kurtz and Sisco cameo in Chouzetsu... but they had a mostly offscreen battle with no real substance to their character, but at least Sisco does flashback to that, so I'll give him that much.
When Burst do use their main characters and their friends for their respective seasons, it's... alright? It was decent in Burst and God, terrible in Chouzetsu, okay-ish in GT, Sparking did it poorly and DB tried... then it didn't. Compare that to MFB, in Fusion, they gave Kenta a few decent focus episodes, Benkei clearly developed. In Masters, all the Gangan members had their moments, albeit not distributed that well. Fury wasn't great but Kenta's character was pretty cool and easy to appreciate there, even if it isn't perfect. Zero G... ehhh honestly I'll give you that, Eight, Kite and Ren were not given very much at all.
My Cho-Z Reaper Deathscyther .12.Cr concept render, click below to see!
No I don't plan on doing more yet.
I should probably go back to making fan custom Zero G beyblade concepts again