Smerel, it definitely is kefirah to think that the fate of the jewish people depends on the bechirah of goyim. Even if their bechira can affect us, it only would be meorer dinim etc… Hashem directly drives the fate of klal yisroel, and according to almost everyone, the individual occurrences of a person’s daily life. To take the pashtus of some of the rishonim who said that not everything that happens is min hashomayim is likewise assur according to most poskim, after that view – if it even ever existed – was completely rejected hundreds of years ago.
But certainly to think that Hashem lets anything happen to klal yisroel without it being a direct gezerah…
By Purim, did anyone think that Haman was just a baal bechirah? It’s preposterous to a believing jew.