There are few differences. Firstly, GPT-3.5 wasn't ahead of Palm etc. from Google which was published at the same time as GPT-4.
Secondly, GPT-4 increased overall AI market. According to all the sources, interviews and leaks, GPT-5 won't be a big leap over GPT-4 as the model size and training data won't be significantly larger. I doubt GPT-5 would do that. (I could be wrong in my assumption though that GPT-5 would just be a incremental gain).
