I don't think Optimus was referring to any specific event there. It was a statement about Megatron's character in general.
While I watched the cartoons I always liked the comics better. My Shockwave is G1 marvel comics Shockwave and you just don't fuck with him! So yeah I'd say he killed them after their little act of defiance. My head cannon does not respect continuity boundaries.
It’s interesting when you watch season 2, and realize just how many characters- major characters- get pushed into the background & nearly completely forgotten about until the movie. Guys like Ironhide, the Dinobots & a ton of others just get saddled with monitor duty, while all the new toys get the bulk of the spotlight. So while it sucks that the G1 fembots only ever got one appearance, it’s the norm for season 2 to ignore even prominent characters.
Agree, I always hated how few lines Thundercracker and Skywarp got in S2 (just too much of Megatron and Starscream squabbling)