People who don't love Dengar usually either don't understand what he adds, or have his modded completely incorrectly. If youre planning a defensive BH team under Bossk, Dengar is pretty much an absolute must. Yes, his personal damage is crap, but his AoE can make or break a battle very early on, and also save your squad multiple times throughout the battle.
Once you have dengar modded correctly, the magic will happen. You want him going after boba and bossk speed-wise, ( at least +80 speed assuming your bossk and boba are better than that ), crit chance of at least 65%, preferably higher, and a potency cross.
The reason for all that CC? You have a total of 7 possible crits on his AoE against 5 enemies, and in 3v3 or late battle its even less, and you always want a minimum of 3 crits. 3 crits will give you tenacity down, stealth for dengar and anti-stealth for the enemy, and 50% TM reduction for the entire enemy squad, plus 5 randomly placed detonators. That is a total of 15 possible debuffs which each recover 5% H/P, meaning one ability will give you 75% health and prot squad wide, as well as possibly stalling the entire enemy team with 50%TM reduction.
Once payouts drop, Dengar will also boost the damage of your other BH when he is stealthed by assisting ( 60% chance when they use a special ability, which happens a lot with boba, embo and jango ), as well as having another 60% chance to call another assist if that enemy is debuffed. Double assist chains happen a lot, and with dispel on embo's basic and double taps on boba and jango, thats a lot more damage ( and possible healing from boba's basic )
Dengar's kit is very complicated, but added to bossk and boba it really makes a BH team get rolling like a runaway train.
Jango is great also, but he really really needs to be g12 with his medpack and furnace for defense use, otherwise he is pretty squishy still. Dengar on the other hand works just fine at g11 or even g10, since he will be under stealth most of the time ( assuming you got his CC up high enough to reliably stealth his first turn )
https://swgoh.gg/squads/117397/
Link to my main BH squad i use for tw/GA defense and dstb if you're interested. I think its the best 5 BH for general purpose use.