I think this is mostly the problem only for the new players (like me) who are still learning the game (more experienced players will probably know which classes they need to beat the bosses and will accordingly plan their levels up) and only for starting period of the game (for app and vet levels) as in the end, while doing champs and dd levels, I will have wide range of classes to experiment with. :)

I've tested your combination and when I feel it is ok indeed but at the same time I think this setup can not be used at its full potential as Crusader can not really often use its the most damaging skill I like, Holy Lance (it needs Crusader to be at rank 3).

I've tested similar setup (Plague Doctor-Crusader-Vestal-Hellion) but it's very tricky - in theory Crusader should start with Holy Lance, but sometimes when there is only two enemies we are in bad position.

I've found YT video with another similar setup but with some more possibilities: Grave Robber-Vestal-Crusader-Lepper. For me it looks promising as we have a possibility to make Crusader 3rd at start of the fight OR not (i.e. Grave Robber can use Lunge at start OR not).

In that setup I mentioned, the crusader is not really meant to use holy lance. He stuns the enemy frontline while the other 3 are taking out one enemy each turn (with crits sometimes two) starting from the back. When 2-3 enemies are dead, you slow down the damage and use healing skills from arbalest and vestal to recover. You could use a hellion on pos1 as well and she stuns even better, but the Crusader brings a very neat stress-heal with "inpiring cry" that comes in handy on longer runs (the vestal may take care of the stunning whenever the crusader wants to use it).

This is by no means the best possible party for anything in particular it's just a blueprint that can be fitted to your needs. The cool thing about this game is that there are dozens of viable combinations each with their own advantages and disadvantages.

This is the tactics I used in the setup I mentioned above: Plague Doctor-Crusader-Vestal-Hellion.

Hellion's "If It Bleeds"/"Iron Swan" and Crusader's "Holy Lance" with a help of Plague Doctor's stuns and blights try to eliminate enemies in back rows as soon as possible. Crusader (after "Holy Lance") begins to stun enemies in front rows. When there are only 2 enemies left then Hellion takes the role of stunner with "Barbaric YAWP!", Plague Doctor mitigates "Barbaric YAWP!"'s debuff with "Emboldening Vapours" and cures any bleeds/blights with "Battlefield Medicine". At the same time Crusader starts to use "Inspiring Cry" to recover whole party from any stress.

Just dropped in to agree with this post. Controlled risk is a great way of summarizing what you need to do in this game. Knowing when you're beaten and need to bug out and knowing when you can push the extra mile even if it costs a hero are the keys to winning along with realizing that skills which do not directly cause damage to enemies can be the most valuable ones in your arsenal.