Yeah, American contractors probably care more about public relations than their Russian counterparts, but neither group is typically upstanding and adherent to laws.
For reference, I made a map of countries engaged in the war against ISIS worldwide (in their various iterations, be it Boko Haram or the Moro Conflict, etc).
That only makes me think ISIS is going to be annihilated faster xD
But their numbers are relatively small. They have 10's of thousands of members, about 2 billion in finances, which is a static figure that they robbed from a single bank, and mostly infantry weapons, that is, Ak-47's, PKM's, dragnuv's etc. Their heaviest equipment is likely mortars, RPG-7's, and armored cars.
They generally lack helicopters, aircraft, or the maintenance crews to service them, as well as tanks and other heavy vehicles. Comparatively, Assad alone has an army of hundreds of thousands, has killed hundreds of thousands, and not only has aircraft, helicopters, tanks, but the latest equipment form Russia, including missiles which could likely take down even American aircraft, such as S-300 missiles, which have a pretty high kill ratio vs. F-16's. Hezbollah has 65,000 members and over 50,000 missiles in their arsenal (having used a lot more) most of which are russian, and constant financing and training by Iran. Russia supplies arms to Iran, so that gives Hezbollah in many ways direct access to Russian equipment. I wouldn't be surprised if S-300 missiles end up in the hands of Hezbollah when fighting Israel any time soon.
I think people, honestly, are overreacting to ISIS. Yes they're bad, but they're the fragmented remains of Al-Qaeda and the Saddam regime. Everyone including their own mums (I.E. Al Qaeda) hates them, so their future doesn't look very bright. Still, they're not a good group of guys. They should certainly go down. ISIS for instance claimed to be a part of Al Nusra, but this was later proven to be false, with Al Nusra rejecting this, so they also seem even crazier than usual. Their bonkers, and people are overreacting to their presence and basically attributing any islamic paramilitary groups in the region, such as Turkey against the Kurds, as basically being ISIS. Even when these groups have denounced any connection, people still continue to assert they're the same group. Thus their military sizes are more or less often over estimated. There's bigger potatoes out there.