To be fair, the criticisms were that they were hired by the DNC after the DNC dragged their feet on giving the FBI access. For some reason they gave this firm the right of way. The original report has also since been revised and had portions retracted... So it wasn't a gold standard of evidence to begin with.
To be fair there are many respectable people (who are strongly anti-Trump) questioning this[1].
1-https://theintercept.com/2016/12/14/heres-the-public-evidenc...