Without looking at any statistics or polling, I think the spoiler effect is not as prominent and is over stated for one reason.
If I’m going out of my way to not vote for the Democrats or Republicans and voting third party that would mean that I dislike my options so much that I’m giving a fuck you to the two party system.
What people can gather from this is if you said there was only two options I would just sit out and therefore it wasn’t going to affect either candidate regardless.
I’m open to be convinced otherwise but I think candidates blaming spoilers should look at the electoral college and themselves when every 4 years they are ready to blame single digit candidates for their losses.
I would agree with you maybe 10 years ago but I think that the empire being in such decline and leading us to the worst candidates back to back to back it’s really hard for me to believe that third parties are to blame for the spoiler effect. Taking third parties off the ballot most likely wouldn’t have the effect that people put on them because everyone has an opinion on the two candidates more than ever.