I haven't actually been counting and probably apparently forgot some (hence the "(?)" in my post), but there haven't been many contacts exclusively introduced by brokers. Of the 4 you listed, it appears 3 are only available via broker according to the wiki, but Dmitri Krylov is introduced by Ashley McKnight.
I'm not saying brokers are entirely redundant, only that you don't generally need to grind brokers to unlock many contacts. May be a matter of perspective - I'm also running each mayhem mission once for badges, so I'm not dealing with them just to get contacts. My impression is that most times I run a mayhem mission I don't get introduced to any new contacts.
Mostly I wanted to balance the multiple mentions of hating the broker system... but honestly I'd recommend newspaper missions over some of the worse story arcs - at least with paper missions you get to choose your own objective so you don't get several consecutive defeat all or escorts. (Edit: and some arcs really don't even have more of a story than the paper missions.)
Edit 2:
At the time I wrote these, I hadn't yet dealt with the brokers in St. Martial. That seems to be the worst area. I ended up going through all the broker-introduced contacts on the wiki to see how many are only introduced by brokers, to see how misleading I'd been, and in total there are 10 contacts that are only listed as "introduced by" brokers: Mr. Bocor, Billie Heck, Angelo Vendetti, Peter Themari, Lorenz Ansaldo, Lt. Demitrovich, Hard Luck, Hardcase, Vivacious Verandi, Regent Korol.
I'm fairly certain I got Vivacious Verandi from the find contacts window, not the broker (Edit 3: verified on another character.) Can't remember earlier contacts well enough to dispute them. Maybe my memory was off, maybe more of them can be had via find contacts.
Edit 4:
Regent Korol is introduced by Westin Phipps, though this isn't listed on the wiki. I have the introduction window open as I'm typing this.
So for St. Martial and Grandville - the part where I've actually been counting - only 2 of the 4 supposedly only introduced by brokers contacts are in fact only introduced by brokers.