I think when it comes to if a boss is "difficult" it does depend on a few things. People tend to say abomination is super easy, and on most cases that is correct, but when it was released with Krampus' Lair, the boss arena was super tight and narrow. This made the minions even more of a threat (this was pre-buff aswell) other maps that follow this mentality is nightmare, the descent, Diesector, Catacombs, Lockdown, Santa's Workshop. However when you play a map like Hostile Grounds, Burning Paris etc, the threat is basically gone since there is so much space to work with and the Abomination's speciality comes from such cramped spaces and being able to completely flood the room.
This tactic can't be said for Patty since he will excel in taking advantage of the open spaces; his machine gun and rockets make good work of that and the artillery strike forces players out of cover, however in a tight and cramped arena, his machine gun would completely miss that one berserker that is hugging Patty.
But for the Matriarch, it is a combination of the both, being able to fight her on maps like Ashwood Asylum, Hellmark Station, Outpost would be better for you since her elec shots asks for good spacing, but the laser demands quick & sharp movements around her to keep out of harms way. When the weapons fail and she gets more aggresive, those tactics fall apart and you're more invited to be in the open and have more free movement as her attacks are more limited. (However the EDARs can go rot in a corner, why were they even introduced in the first instance). Other than the questionable EDARs, the Matriarch is just fine as she is besides her really stale animations.
Other than which boss you get given on which map, it does come due in part with perk selection; Commando can spot out Patty and Matty, Demo shreds the KFP, medic is the medic, and GS can slow the approach of bosses with well placed shots. And I think this is where the problem lies; being able to have a perk that can fill a role PROPERLY, when I first approached the SWAT, I thought it would be either the tank or the utility, but the armour doesn't stick around long enough to make that viable, and the stumble power just isn't enough to be utility against larger zeds. Other than the SWAT, the SV is just a weird class to pick (and almost all SV allies I get are rubbish) the SS is only "viable" when they are level 25 to help proc Zed time.
Once they stop giving the Firebug, Medic and Berserker all the OP toys, perhaps they can look into making the SWAT more of a tank/crowd control, the Survivalist more flexible and the medic to not be such a clutch.
If they can do anything with the bosses, make the abomination faster and doesn't fall over (what the actual sht is that?) don't have the Patriarch retreat to heal, similarly to PvP Patriarch that can heal on the spot, and bring proper FP to the KFP boss fight aswell as Quarter Pounds. I get what they are trying to do with KFP and Abom, with a boss with a lot of minions or some big beefy minions that can deal some trouble, so make them more troublesome!