The report isn't written by Michael Morell, the aforementioned 30 year etc., but "co-authored", and the whole thing was sponsored by Coinbase and Square. Who pays the piper, and all that. And if you want to use his CIA experience as authority: his expertise was counter-terrorism, not "normal" crime, and he defended the use of drone strikes and torture.

Their evidence is: "the firms we spoke with believe the unseen illicit activity is relatively small". That's it. The confident conclusion that it's overstated doesn't even allow you to infer if it's more or less than 50%; it doesn't even say which statistic they actually used.

If it's total percentage of transactions or sum of traded bitcoins, that isn't even that important: you can amass a small fortune in just a handful of transactions, whereas trading bitcoin for investment generates many more transactions, all completely irrelevant to the influence of bitcoin on crime.

There are other quotes from experts available, such as “Bitcoin — and virtual currency in general — is widely used in the trafficking of weapons and drugs, and in ransomware and extortion cases. It is used a lot by criminals.”