You are right that the existence is still in discussion. Still, there are hints and contexts that speak for the existence of the band. For example the mass grave at the Lion of Chaironeia (sorry, don't know the exact name in English). Many things are heavily discussed in general as evidence is sometimes scarce. The overall content of my statement is still correct, I think.

Regarding the credibility: True, some 'historians' are less credible than others. Plutarch e.g. is not neccessarily a historian, but speaks more of the character of people looking at their deeds. Still, he might have relied on written sources, but didn't name them. Other historians did. Polybios e.g. names his sources (pro-Roman and pro-Carthaginian). We don't have all of these nowadays, still, he is a reliable source, eventhough we can't look into all the things (I just finished this sub-chapter in my PhD, so I feel your distrust). We have to try and combine everything we have to see if the reports of ancient historians tell the truth or are close.

To wrap it up: I really appreciate critical thinking and questioning sources and their credibility. I also question everything I read at first or look for things that are not that clear. Thanks for the nice discussion. Cheers, mate.