I would like to fight against ally bosses more difficult, as it if were Titan. That could be more exciting, where you will need do a strategy with your partner. Actually, merged dragonoid and nightmare captain shoggoth are too easy.
Can we imagine a boos with spreadfire i[8|]n his gun? Or maybe another passive core. It could be a really challenge. [:-]
To add on to what lord ginger is saying take admin 10 and exile leader for example. These bosses were made to be hard when passives were a thing and they were just that. challenging and hard. However the moment passives went active these bosses became a massive joke due to being able to use passive turned actives against them.