Thinking back to when I was raiding at that level, I found the most annoying of those to be Boldtusk with emblems. I was shocked how often his revive fired and allowed him to get off his healing special. He’s a tough nut to crack to begin with, and having that happen 2 or 3 times in a row is just demoralizing. Plus, the attack buff makes the rest of the team more dangerous.
On offense, I usually run two healers, so it took me a long time to realize that healers on defense are not always super helpful. I ran Melendor +20 on the wing until last week. I just replaced him with my near-max Vela, and the results have been better so far. Healers on the wings usually don’t charge fast enough to heal your team before the core is dead anyway, and Melendor and Sabina are kind of squishy to start with, so it’s not like they’ll be stalwarts holding on for the victory as the last man/woman/zombie standing. I hear Elkanen can pull this off sometimes, though.
Typically, the tank needs to be a hero that you are afraid to see go off, emphasizing the need to kill them quickly. Healers aren’t really that, since they just stall for time, unless there is some serious firepower behind them. Colen is a dangerous tank to a point, but then he becomes too squishy. Same can be said of his five-star equivalent, Azlar, who is really scary when he fires. Grimm is far too fragile to be a tank, and I don’t really see Caedmon being that great either. (Sonya does the same thing and survives better, but doesn’t hit as hard.) Gormek, though, I used at tank for a while. He’s got a ton of HP, which gives him a good chance to fire, and even if he dies right after, his defense down ailment lasts 6 turns if not cleansed. That can feel like an eternity with sufficient firepower behind him. A Gormek tank with a Caedmon flank could work at the four-star level. Caedmon is strong against blue, so if the opponent stacks blue against Gormek, they’ll have a harder time taking down Caedmon. Plus, Caedmon is fast mana and hits decently hard, especially if he fires after Gormek’s defense down.
Unfortunately for you, Guvnor is pretty much right. If I were picking a four-star tank, I’d probably go with Boril. Riposte basically has to be dispelled, so you force the opponent to bring a dispeller or two, and those are thin in the classic five-star ranks, so you are forcing them to bring four-stars to the fight. Also, Boril’s hit may be anemic, but his defense, especially with emblems, makes him dang near immortal; it’s conceivable he could fire 2 or 3 times before dying, depending on the board. Here’s my Boril +20 for reference: