There are several good reasons to believe that what Crowdstrike reported about the DNC server need to be independently reviewed.
1. The information they used to verify that Gucifer 2.0 was the Russian hacker was so amateurish that it almost looked like he was putting a label on the hack to point to Russia.
2. The FAT block data on the Wikileaks emails indicate they were locally copied from their original source not transferred over higher latency internet connections. The VIPS organization that did this analysis has briefed Sec. Pompeo and is awaiting feedback on their conclusions.
3. It makes no sense for a Russian spy agency to hack the emails and then give them to Wikileaks. Besides raising their visibility unnecessarily it nullifies any true blackmail or coercion potential they might have and is just not the way intelligence agencies work. They don’t care who wins elections, they only want to control or influence whoever wins.
4. Julian Asange himself has denied the emails came from a state actor like Russian and confirmed that it was from a DNC insider source. One published news report that was based on a personal meeting with Asange indicated this person was Seth Rich but the story has since disappeared on the internet and can not be confirmed.
It was independently reviewed. By the FBI.
All of the forensic materials gathered by Crowdstrike, including images of the servers and data storage, were shared with the FBI who conducted their own analysis - which agreed with Crowdstrike's.