The prosecutor (Shokin) was considered to be corrupt, and his firing was supported by the European Union and the IMF.
In fact, the investigation into Burisma
was not occurring under Shokin (
Link), and in any case, only concerned events that pre-dated Hunter Biden's involvement in the company (
Link).
Now if you want to say that Biden's son getting a kush job he's not qualified far is swampy and a bad look, go for it. I would agree. But there is no evidence (and in fact, evidence to the contrary), that the prosecutor's firing was in no way related to protecting Hunter Biden.