Been playing the game some more. If there's one saving grace it's that it DOES scale somewhat in difficulty once you start doing tougher missions. I guess maybe I notice it more than some because I'm playing my first run through as bare bones as I can equipment wise to compensate for only being on Normal mode.
The only thing I've bought so far is a $1200 assault rifle, at the start of the game where they send you to a gun shop. For the most part I use whatever I pick up though. Some convoys can be tough if you have minimal gear and aren't careful how you do them. Like No Rules, which has a big wig mob boss and an entourage of limos, SVUs, and heavily armed and armored troops.
I ended up parking a courier van sideways across their lane on one end of a raising platform type bridge and activated the bridge as the target limo was on the center of the platform. This isolated the lead SVU and the target limo on my side of the bridge after they drove off the platform.
Taking cover from behind the van, they didn't even see me, making it an easy mop up with my SVD and SGR 12, followed by a quick rush at the target to get the requisite knock down. Other attempts from various vantage points with the SVD failed due to civilians calling cops and my getting caught in the middle of their battle, and/or getting flanked by either after re-positioning.
So it will no doubt be necessary to get very clever or gear up on higher difficulty modes, maybe both.