How did Waspinator get back to Cybertron? He doesn't have FTL capability, he doesn't technical know-how. Did he really go The Slow Path back to Cybertron? Just in time to be captured by Megatron?
No, its entirely possible that he landed much earlier, and simply laid low for a few vorns. Of course, given how much Cybertron moved around over the course of G1, and presumably thereafter, its entirely possible that he arrived shortly before Megatron's takeover simply because he couldn't remember where the planet was supposed to be until around then.
AFAIK, he went back to Cybertron after finding the rest of the survivors. This is told on one of the comics post-Beast Wars.
The real question is, when did he arrive on Cybertron? Depending on how long he traveled, he might have even arrived before the Great Upgrade...
I seem to remember reading on TFWiki.net that Waspinator was the Darksyde's pilot. Perhaps he cobbled something together out of spare Transwarp cells and a stasis pod.
On a similar note and all fan theories aside, just how did Megatron get so anti-organic? He showed no such resentment for most of his battles in Beast Wars, and actually seemed quite comfortable with his beast modes in general. Heck, with the power of his Dragon mode, he could defeat Optimus Primal in EVERY confrontation they had afterwards, with elemental strength. Why would he grow to hate something that gave him such power and the ability to overcome most of his enemies?
There was a Botcon script reading (or something like that) not long ago that involved Beast!Megatron interacting with Animated!Optimus and Sari on an AU!Cybertron. Maybe Sari's behavior during that is what convinced Megatron to be anti-organic.
By the end of Beast Wars, he's pretty vehemently anti-organic and pro-God!Megatron. Being lost on Cybertron for untold ages as the sole organic transformer might well have driven him over the edge.
If Rattrap had such a big problem with his lack of built-in weapons, why didn't he just pick up a gun? His old weapons, aside from his transmetal tail that he rarely used, weren't built-in, so it's not like things have changed that much. They're on a deserted Cybertron and continuously tearing heavily armed war drones to scrap, so it can't possibly be that hard for him to scavenge either a working weapon or the parts to make one. He's shown to keep around a variety of tools and made those seed bombs as well, but a reliable energy weapon would be far more efficient than lobbing grenades one at a time. Was it just another example of the writers forgoing logic in the name of an overly simplistic theme?
Long story short? Writer on Board in the form of Bob Skir. In one of his old interviews, Skir admitted that he preferred that the heroes he writes for won't use guns. He wasn't exactly against firearms since he said that characters like The Punisher need to use guns as part of their character. However, he was of the belief that Maximal heroes like Optimus and Rattrap aren't absolutely required to have guns... which can make sense for a character like Optimus who has his strength and sword/mace-fighting skills to make up for not having firearms but absolutely no sense for Rattrap whose Establishing Character Moment for his entire Beast Wars/Transformers tenure was that of a gun aficionado and expert marksman.
At one point Nightscream makes a Tonka reference. I'm pretty sure he's never left Cybertron, much less ever been to Earth. Did Optimus Prime and the rest of the G1 Autobots really add this idiom to the culture upon returning?
Another episode has Nightscream and Silverbolt making a Monopoly reference. Same point.
Earth was very important to Cybertronian history. It's likely they've had a LOT of contact over the centuries, maybe even into their modern day, we just don't see it since Beast Wars largely took place in the past. It's not surprising Earth culture has seeped into Transformer consciousness.