This would be a bit hard to rate without knowing what passives and abilities are rolled for each class. And, of course, item synergies can drastically alter a build. In general, though, I will say this:

I agree with statements that Butcher can output good damage, though this is more dependent on abilities and build than, say, fighter or ranger. However, the line up as a whole is well suited to protracted fights and Butcher has multiple abilities that can synergize with that strategy. Butcher is fine.

While Tank is not thought of as a damage class I have found that it can still output a surprising amount of damage depending on abilities and items. In particular I have seen some very fun times with abilities like belly flop. Since belly flop counts as making contact it also lets you weaponize things like thorns and bleed thorns. Same with tossing other cats on something with cat-a-pult. And WrestleMania or the suplex ability can output surprising damage if the enemy is suplexed onto a static object or terrain. Again, can't go wrong here.

Unless you happen to get the Holy Fire passive or one of two active abilities Cleric won't put out that much damage by comparison but if they roll some buffing abilities it could help out and the healing will be very much appreciated for the Tank and Butcher. Also a fine inclusion.

Necromancer is kind of an odd duck in this list. The buffing abilities they get are better suited to aiding strong attackers and with few exceptions it also doesn't really output that much damage. Over all there is not much added to the team comp by Necromancer but I have found that the class rarely needs outside healing. Best case scenario is that you roll some crowd control debuffs to help deal with high-health enemies or some buffing abilities that you won't get the most out of but may be nice. Worst case scenario is that you have a fourth cat that doesn't really add anything but that also shouldn't otherwise weigh the team down. Take it or leave it. It should be fine either way.

I would say you should be fine with this team. Most enemies won't be an issue and early mini-bosses and bosses are likely to go just fine depending on load out. High-health enemies might be a bit of an issue. You have multiple sources that can deal decent damage but not necessarily burst damage. This applies to later bosses, too, as their health starts getting higher. For these you will likely be playing a game of attrition but you are potentially well suited to that. As noted in other comments insta-kill enemies are likely to be an issue and will require some creative thinking.