I'll post this link again in case anyone missed it. The TFwiki page on G1 Cyclonus in the G1 cartoon continuity dedicates six paragraphs into the problems with Cyclonus' former identity. You fine folks know how to follow a hotlink so I'm not going to post my own spiel which would be nothing more than just rewording what's already stated on that wiki page (you can read it for yourselves).

The "because Bombshell's in front" isn't a great argument because directions in space is completely relative.

And how do you know it was Bombshell and not Salvo or any of his other clones?
Anyway, if you want to believe it's Bombshell or Salvo (etc.) then go right ahead.

More Personal Opinion That's Not Canonical Fact:
Another reason why I prefer the Skywarp explanation is because Cyclonus' personality is more like Skywarp's and very different from Bombshell's. In the G1 cartoon Skywarp was portrayed as being a loyal soldier to Megatron. Starscream was the traitor and Thundercracker was somewhat indifferent, but Skywarp was the loyalist. We can see this in The Ultimate Doom where Skywarp and Starscream fight in the lift over the "brilliance" of Megatron's plan. G1 cartoon Cyclonus is also fiercely loyal to Galvatron. This is quite different from Bombshell who, like the other Insecticons in the cartoon, is a pure opportunist. He's only ever loyal to Megatron so long as it suits his purposes. So to me Cyclonus being the evolution of Skywarp makes sense to me as much as Galvatron is the evolution of Megatron. They share personality traits. Again, I recognise that this is purely my own opinion and not a decisive canonical fact.